System and method for joint resurface repair

ABSTRACT

A generic bone implant, or set of standardized implants, is created based on using a guide device to develop an axis normal to an articular surface of bone and collecting only one or two data points. A generic cutting tool is used to cut the bone to a point where a generic implant can be used. Several improved tools relating to the procedure for using such an implant, as well as methods for using implants consistent with the invention are further described, including: single-axis and biaxial drill guide tools and methods, generic single-axis implant methods and devices, generic biaxial implant methods and devices, tools and methods for holding or delivering an implant, removal or revision tools and methods, digital measuring systems and methods, and set of measuring gauges for determining the appropriate implant dimensions.

[0001] This application is a continuation-in-part application under 37C.F.R § 1.53(b) of application Ser. No. 09/846,657, filed May 1, 2001,which claims priority from U.S. provisional application Serial No.60/201,049, filed May 1, 2000.

FIELD OF THE INVENTION

[0002] This invention relates to devices and methods for the repair ofdefects that occur in articular cartilage on the surface of bones,particularly the knee.

BACKGROUND OF THE INVENTION

[0003] Articular cartilage, found at the ends of articulating bone inthe body, is typically composed of hyaline cartilage, which has manyunique properties that allow it to function effectively as a smooth andlubricious load-bearing surface. However, when injured, hyalinecartilage cells are not typically replaced by new hyaline cartilagecells. Healing is dependent upon the occurrence of bleeding from theunderlying bone and formation of scar or reparative cartilage calledfibrocartilage. While similar, fibrocartilage does not possess the sameunique aspects of native hyaline cartilage and tends to be far lessdurable.

[0004] Hyaline cartilage problems, particularly in knee and hip joints,are generally caused by disease such as occurs with rheumatoid arthritisor wear and tear (osteoarthritis), or secondary to an injury, eitheracute (sudden), or recurrent and chronic (ongoing). Such cartilagedisease or deterioration can compromise the articular surface causingpain and further deterioration of joint function. As a result, variousmethods have been developed to treat and repair damaged or destroyedarticular cartilage.

[0005] For smaller defects, traditional options for this type of probleminclude non-operative therapies (e.g., oral medication or medication byinjection into the joint), or performing a surgical procedure calledabrasion arthroplasty or abrasion chondralplasty. The principle behindthis procedure is to attempt to stimulate natural healing. At the defectsite, the bone surface is abraded, removing approximately 1 mm. or lessusing a high-speed rotary burr or shaving device. This creates anexposed subchondral bone bed that will bleed and will initiate afibrocartilage healing response. Although this procedure has been widelyused over the past two decades and can provide good short term results,(1-3 years), the resulting fibrocartilage surface is seldom able tosupport long-term weight bearing, particularly in high-activitypatients, and is prone to wear.

[0006] Another procedure, referred to as the “microfracture” technique,incorporates similar concepts of creating exposed subchondral bone.During the procedure, the cartilage layer of the chondral defect isremoved. Several pathways or “microfractures” are created to thesubchondral bleeding bone bed by impacting a metal pick or surgical awlat a minimum number of locations within the lesion. By establishingbleeding in the lesion and by creating a pathway to the subchondralbone, a fibrocartilage healing response is initiated, forming areplacement surface. Results for this technique are generally similar toabrasion chondralplasty.

[0007] Another known option to treat damaged articular cartilage is acartilage transplant, referred to as a Mosaicplasty or osteoarticulartransfer system (OATS) technique. This involves using a series of dowelcutting instruments to harvest a plug of articular cartilage andsubchondral bone from a donor site, which can then be implanted into acore made into the defect site. By repeating this process, transferringa series of plugs, and by placing them in close proximity to oneanother, in mosaic-like fashion, a new grafted hyaline cartilage surfacecan be established. The result is a hyaline-like surface interposed witha fibrocartilage healing response between each graft.

[0008] This procedure is technically difficult, as all grafts must betaken with the axis of the harvesting coring drill being keptperpendicular to the articular surface at the point of harvest. Also,all graft placement sites must be drilled with the axis of a similarcoring tool being kept perpendicular to the articular surface at thepoint of implantation. Further, all grafts must be placed so that thearticular surface portion of these cartilage and bone plugs is deliveredto the implantation site and seated at the same level as the surroundingarticular surface. If these plugs are not properly placed in relation tothe surrounding articular surface, the procedure can have a verydetrimental effect on the mating articular surface. If the plugs areplaced too far below the level of the surrounding articular surface, nobenefit from the procedure will be gained. Further, based on therequirement of perpendicularity on all harvesting and placement sites,the procedure requires many access and approach angles that typicallyrequire an open field surgical procedure. Finally, this procedurerequires a lengthy post-operative non-weight bearing course.

[0009] Transplantation of previously harvested hyaline cartilage cellsfrom the same patient has been utilized in recent years. After thecartilage is removed or harvested, it is cultured in the lab to obtainan increase in the number of cells. These cells are later injected backinto the focal defect site and retained by sewing a patch of periostealtissue over the top of the defect to contain the cells while they healand mature. The disadvantages of this procedure are its enormousexpense, technical complexity, and the need for an open knee surgery.Further, this technique is still considered somewhat experimental andlong-term results are unknown. Some early studies have concluded thatthis approach offers no significant improvement in outcomes overtraditional abrasion and microfracture techniques.

[0010] U.S. Pat. No. 5,782,835 to Hart et al. discloses an apparatus andmethod for repair of articular cartilage including a bone plug removaltool, and a bone plug emplacement tool. The method of repairingdefective articular cartilage includes the steps of removing thedefective cartilage and forming a hole of sufficient depth at the site.A bone plug comprising intact bone and cartilage adhering thereto isremoved from a bone lacking defective cartilage is placed in the hole atthe site of the damage.

[0011] U.S. Pat. No. 5,413,608 to Keller discloses a knee jointendoprosthesis for replacing the articular surfaces of the tibiacomprising a bearing part which is anchored on the bone having an upperbearing surface and a rotatable plateau secured on the bearing surfaceand forming a part of the articular surface to be replaced. A journalrises from the bearing surface and cooperates with a bore in the plateauto provide lateral support.

[0012] U.S. Pat. No. 5,632,745 to Schwartz describes a method ofsurgically implanting into a site a bio-absorbable cartilage repairassembly. The assembly includes a bio-absorbable polygonal T-shapeddelivery unit having radial ribs to be mounted in the removed area and aporous bio-absorbable insert supported by and in the delivery unit. Themethod comprises the steps of preparing the site to receive the assemblyby removing a portion of the damaged cartilage and preparing the site toreceive the assembly by drilling and countersinking the bone. Theassembly is inserted and seated using an impactor in the drilled andcountersunk hole in the bone until the assembly is flush with thesurrounding articular surface.

[0013] U.S. Pat. No. 5,683,466 to Vitale illustrates an articular jointsurface replacement system having two opposing components. Eachcomponent has a tapered head piece for covering the end of a bone andfor acting as an articular surface, an integrally formed screw stem ofsufficient length to extend into the bone and inwardly angled bone gripson the underside of the head piece to allow fixation to the bone bycompression fit. The partially spherical convex shaped exterior of thefirst component complements the partially spherical concave shapedexterior of the second component.

[0014] U.S. Pat. No. 5,702,401 to Shaffer discloses an intra-articularmeasuring device including a hollow handle defining a first passagewayand a hollow tube having a second passageway extending from the handle,the hollow tube carrying a projection at its distal end for seating on afixed site and a probe disposed at the distal end of the hollow tubewhich may be directed to a second site, to enable measurement of thedistance between the first and second sites.

[0015] U.S. Pat. No. 5,771,310 to Vannah describes a method of mappingthe three-dimensional topography of the surface of an object bygenerating digital data points at a plurality of sample points on saidsurface, each digital data point including a property value and aposition value corresponding to a particular point representing theproperties of the surface of the object. A 3-D transducer probe (e.g., adigitizer) is moved on or over the surface along a random path, and thesample points are digitized to generate a real-time topography or map ona computer screen of selected properties of the object, includingwithout limitation, surface elevation, indentation stiffness, elevationof sub-surface layers and temperature.

[0016] Prosthetics for total knee replacement (TKR), whereby the entireknee joint or a single compartment of the knee joint is replaced can bea common eventuality for the patient with a large focal defect. Althoughthese patients are also managed with anti-inflammatory medications,eventual erosion of the remaining articular cartilage results ineffusion, pain, and loss of mobility and/or activity for the patient.Problems encountered after implanting such prostheses are usually causedby the eventual loosening of the prosthetic due to osteolysis, wear, ordeterioration of the cements used to attach the device to the hostbones. Further, some prostheses used are actually much larger than thedegenerated tissue that needs to be replaced, so that extensive portionsof healthy bone are typically removed to accommodate the prostheses.Patients who undergo TKR often face a long and difficult rehabilitationperiod, and the life span of the TKR is accepted to be approximately 20years. Accordingly, efforts are made to forgo the TKR procedure for aslong as possible.

[0017] Accordingly, there is a need for an improved joint surfacereplacement system that would be effective in restoring a smooth andcontinuous articular surface and that would also be as durable as theformer hyaline cartilage surface, within the context of a minimallyinvasive procedure that allows for a nearly immediate return toactivity, restoration of lifestyle, and pain relief.

SUMMARY OF THE INVENTION

[0018] The present invention provides tools and methods for mapping andmeasuring the articular surface of a joint (or of any bony surface) andfor fabricating a prosthetic device based on this recorded data.

[0019] In one method consistent with the invention, once the defect ofthe chondral surface has been identified, a guide pin is insertedarthroscopically. A fixation screw having a tapered distal tip and anaggressive distal end thread form is then driven into the subchondralbone in relation to a reference axis that is approximately central tothe defect. The fixation device also serves to define a tangent point tothe surrounding articular surface. The screw is driven by a socket typedriver that engages a hex-shaped proximal extension. A furthercylindrical proximal extension of the screw (or other mating feature,e.g., a recess in the screw) that eventually serves as a fixationelement for the surface prosthetic is at this time concealed with acover (or other mating feature corresponding to the mating feature ofthe screw, e.g., a plug for mating with a screw having a recess as itsmating feature) having a radiused proximal end. One or more milled slotsrun the length of the uniform diameter portion of the screw.

[0020] Under arthroscopic view, the screw depth is adjusted so that theradiused cover surface is positioned tangent to the radius that definesthe existing articular surface. At this time, the guide pin is removedand the knee is articulated. The depth positioning of the radiused coverestablishes an origin or reference point for all future measuring,cutting, and prosthetic machining operations. Arthroscopic examinationis carried out to confirm positioning.

[0021] A measuring tool is inserted on the reference axis. A centralelement of the measuring tool is a static post that establishes theaxial location of origin. By rotating the outer arm or outrigger of themeasuring tool relative to the static post while also maintainingcontact with the articular surface, an axial displacement or Z dimensioncan be established relative to the origin for any point along the knownradial sweep of the outrigger to determine the final geometry of theprosthetic surface which fits within the defect. These Z dimensions canbe recorded in real time with conventional dial gauge indicators, orwith digital recording devices, or by using marking techniques. Althoughnumerous points may be taken, ideally a minimum number of points aretaken to accurately define the target articular surface.

[0022] Locating surfaces or features created on the screw, (oralternatively, on the radius cover, as described in alternativeembodiments herein), correlate to some surface or feature on themeasuring tool and allow the measurement of the rotational position ofthe points about the axis with respect to the locating surfaces. Datarecorded during the mapping procedure can then be entered intoparametric engineering design software or similar algorithm to define athree dimensional surface matched to the bearing surface geometry to beimplanted and reproduce the anatomic contours mapped.

[0023] An alternative measuring device for obtaining the articularsurface dimension includes an outer marking element and an innerrecording element. The marking element includes a sharp indentingmechanism which when pressed by the surgeon creates a depression or markin the relatively soft surface of the recording element, which deformsat these marked points so that they can be utilized as patient data. Therecording element also includes a surface that corresponds to thesurface of the proximal extension of the fixation screw. During themapping procedure, data points are established of the rotationalposition of the mapped articular surface relative to the screw. Thesedata points are translated to the implant geometry so that the accuraterotational location of the implant relative to the screw is maintained.

[0024] In order to secure the implant to the fixation screw, a precisiontaper (or other component of a mating feature) is machined into aprotrusion (or other component of a mating feature) on the back of thedevice. The implant may be constructed of cobalt chromium, or othermaterials. The implant may also include a slight outward taper orprotrusion along the diametrical surface to enhance load bearing or loadtransfer properties of the implant to surrounding bone. Additionally, aseries of radial cuts may create surfaces that increase resistance ofthe implant to rotational forces. These features may be located aroundthe outer diameter of the implant.

[0025] In another aspect, the invention includes a compass instrumentfor measurement and surface preparation of the implant target sitesubsequent sizing of the implant. This compass instrument is configuredso that it can be delivered to the site arthroscopically, and whencoupled to the axis defined by the guide pin it can be used formeasuring and cutting operations.

[0026] In another embodiment, the compass instrument consists of ahandle, a cannulated shaft that extends through the handle, and acannulated distal offset arm configured to serve as a linearlyadjustable mounting tool for a series of cutting blades, boring blades,or measuring probes.

[0027] With the guide pin advanced through the instrument shaft, whenfitted with a blade, a fixed length from the rotational or referenceaxis to the cutting blade's cutting surface is established. This definesthe radius that is effected as the instrument is rotated around theguide pin, and corresponds to the overall diameter of the implant. Thissharp cutting blade is used to circumscribe and cleanly cut thesurrounding articular cartilage.

[0028] In another aspect, the invention features a bone cutting orscoring instrument whereby the bone-cutting instrument is positioned onthe guide pin reference axis and is used to prepare the target site tomatch in configuration and dimension the contacting surface of theimplant. The matching fit between the bone surfaces of the preparedtarget site and the bone contacting surfaces of the implant canadvantageously ensure long term clinical results with the implant, aspoor quality of fit between bone surfaces and bone contacting surfacesof traditional orthopedic prosthetic devices has been noted tocontribute to early clinical failures.

[0029] Following fabrication of the implant, a second surgical procedureis performed. The radiused cover is removed exposing a precision taper(or, alternatively, the cover may be removed during the firstprocedure). A pin with a distally mounted element is placed through thecentral lumen of the fixation screw so that the distally mounted elementis secured into the screw. This element carries one or more suturestrands that now trail from the fixation screw. The sutures are thenthreaded through the implant and a knot or bead may be created proximalto the implant. By continuing to manipulate and tension the suturestrands, the implant can be brought coaxial to the fixation screw. Oncecoaxial, the implant is aligned via engagement of the keyed elements anddriven into place with a plastic driving rod and mallet. Finally,through the guide aperture on the surface of the implant, bone cementmay be injected to enhance the contact surface between the implant andthe subchondral bone.

[0030] In another aspect, the invention further features a driverwhereby the implant is connected to the driver via a holder and a tetherelement, such as a suture or wire. The implant and the driver are theninserted arthroscopically. Tension is then applied to the tether elementso that the implant is drawn back and seated on the driver. The implantcan then be controllably delivered to the prepared target site. The seatportion of the driver may comprise a material that may be impacted toseat the implant without damaging the implant surface.

[0031] In one aspect, a guide device for locating a guide pin or wiresubstantially normal with respect to an articular surface of bonecomprises a cannulated shaft having a distal end and a centrallongitudinal axis; and a ring portion coupled to the distal end of theshaft, the ring portion comprising a planar distal contact surfacecomprising a plurality of points radially extending from any given pointalong the central longitudinal axis of the shaft.

[0032] In another aspect, a guide device for locating a guide pin orwire substantially normal with respect to an articular surface of bonehaving an anterior-posterior (AP) curve and a medial-lateral (ML) curvecomprises a cannulated outer shaft and a cannulated inner shaft. Theouter shaft has a central longitudinal axis and an outer component atits distal end, the outer component comprising a set of arms, and thecannulated inner shaft is slidably disposed within the cannula of theouter shaft, the inner shaft having an inner component at its distal endand sharing the central longitudinal axis of the outer shaft, the innercomponent comprising a set of arms.

[0033] In method form, a method for replacing a portion of an articularsurface of bone comprises defining an axis generally normal to theportion of an articular surface of bone to be replaced; excising atleast the portion to be replaced by cutting the articular surfaceradially symmetrically about the axis, thereby creating an excisedportion of the articular surface; selecting an implant corresponding tothe dimensions of the excised portion from a set of variously-sizedimplants; and installing the selected implant into the excised portion.

[0034] In method form, a method for replacing a portion of an articularsurface of bone having an anterior-posterior (AP) curve and amedial-lateral (ML) curve comprises defining an axis generally normal tothe portion of an articular surface of bone to be replaced using ananterior-posterior (AP) curve and a medial-lateral (ML) curve of thearticular surface; excising at least the portion to be replaced bycutting the articular surface radially symmetrically about the axis,thereby creating an excised portion of the articular surface; selectingan implant corresponding to the dimensions of the excised portion from aset of variously-sized implants; and installing the selected implantinto the excised portion.

[0035] In a further aspect, a tool for holding an implant comprises anactivatable suction source; and an elastomeric suction tip adapted toreceive an implant, the tip being coupled to the suction source.

[0036] In method form, a method for holding an implant comprisescoupling a suction source to an implant; and activating the suctionsource.

[0037] In method form, a method for delivering an implant comprisescoupling a suction source to an implant; activating the suction source;approximating the implant to its delivery site; and applying a force tothe implant in the direction of the delivery site.

[0038] In yet another aspect, a tool for removing an implant from itsdelivery site comprises a cylindrical structure having a distal end; thedistal end comprising a longitudinal central axis, a circular bladeportion having a leading edge comprising a blade surface turned on thedistal-most portion, and a lip portion disposed proximally with respectto the leading edge; and a plurality of slits parallel to thelongitudinal central axis of the distal end formed along the length ofthe cylindrical structure, so as to permit sufficient outward expansionof the distal end to accommodate the top edge of an implant therein.

[0039] In method form, a method for removing an implant from itsdelivery site comprises disposing the lip portion of the leading edge ofthe distal end of a removal tool over the upper edge of an implantseated in its delivery site; and applying a pulling force to the removaltool.

[0040] In still another aspect, a device for mapping a portion of anarticular surface of bone comprises a handpiece, an inner shaft, acontact tip, a rotary measuring element, and a linear measuring element.The inner shaft runs along the length of and is disposed within thehandpiece and comprises a mating feature for mating with a fixed elementlocated substantially normal with respect to an articular surface. Thecontact tip is slidably and rotatably disposed about the inner shaft.The rotary measuring element is coupled to and rotating with the contacttip. The linear measuring element is nested concentrically and coaxiallyto the rotary measuring element, and coupled to and moving linearly withthe contact tip.

[0041] A generic bone implant, or set of standardized implants, mayfurther be created based on using a guide device to develop an axisnormal to an articular surface of bone and collecting only one or twodata points. A generic cutting tool may be used to cut the bone to apoint where a generic implant can be used. Several improved toolsrelating to the procedure for using such an implant, as well as methodsfor using implants consistent with the invention are further describedhereinbelow, including: single-axis and biaxial drill guide tools andmethods, generic single-axis implant methods and devices, genericbiaxial implant methods and devices, tools and methods for holding ordelivering an implant, removal or revision tools and methods, digitalmeasuring systems and methods, and set of measuring gauges fordetermining the appropriate implant dimensions.

DESCRIPTION OF THE DRAWINGS

[0042]FIG. 1 is a fragmentary side view of a knee having therein anexemplary assembled fixation device and implant of the joint surfacerepair system surgically implanted by the method in one embodiment ofthe present invention;

[0043]FIG. 2a is an exploded side view of an exemplary fixation screwand hex-shaped proximal extension in one embodiment of the presentinvention;

[0044]FIG. 2b is an exploded perspective view of an exemplary fixationscrew and hex-shaped proximal extension in one embodiment of the presentinvention;

[0045]FIG. 3a is a side view of an exemplary assembled fixation screwand hex shaped extension in one embodiment of the present invention;

[0046]FIG. 3b is an exploded perspective view of another exemplaryfixation screw and implant in one embodiment of the present invention;

[0047]FIG. 4a is a perspective view of the upper surface of an exemplaryimplant in one embodiment of the present invention;

[0048]FIG. 4b is a side view of an exemplary implant in one embodimentof the present invention;

[0049]FIG. 4c is a perspective view of the lower surface of an exemplaryimplant in one embodiment of the present invention;

[0050]FIG. 5a is a side view of an exemplary assembled fixation deviceand implant in one embodiment of the present invention;

[0051]FIG. 5b is a perspective view of an assembled fixation device andimplant in one embodiment of the present invention;

[0052]FIG. 5c is a perspective view of the upper surface of an exemplaryimplant, in one embodiment of the present invention;

[0053]FIG. 5d is a perspective view of the lower surface of an exemplaryimplant, in one embodiment of the present invention;

[0054]FIG. 6a is a sectional view of a knee having damaged articularcartilage, showing an exemplary guide pin drilled into the centralportion of the defect and an arthroscope being disposed adjacentthereto, in a surgical procedure consistent with one embodiment of thepresent invention;

[0055]FIG. 6b is a side view of the distal tip of an exemplary drilldevice for boring a pilot hole to receive an exemplary fixation screw,in one embodiment of the present invention;

[0056]FIG. 7a is a sectional view of a knee having damaged articularcartilage, showing an exemplary fixation screw being driven into thedefect by an exemplary socket type driver arranged on the guide pin, ina surgical procedure consistent with one embodiment of the presentinvention;

[0057]FIG. 7b is a side view of the exemplary fixation screw, sockettype driver and guide pin of FIG. 7a, illustrating the hex shapedproximal extension in a cross-sectional view, in a surgical procedureconsistent with one embodiment of the present invention;

[0058]FIG. 8a is a perspective view of a knee having damaged articularcartilage, showing an exemplary fixation screw and hex-shaped proximalextension implanted in the defect after removal of an exemplary sockettype driver and guide pin, in a surgical procedure consistent with oneembodiment of the present invention;

[0059]FIG. 8b is a sagital view of the exemplary fixation screw andhex-shaped proximal extension of FIG. 8a implanted in the defect afterremoval of an exemplary socket type driver and guide pin, in a surgicalprocedure consistent with one embodiment of the present invention;

[0060]FIG. 8c is a perspective view of an exemplary fixation screw,proximal extension and cover, in one embodiment of the presentinvention;

[0061]FIG. 9a is a sectional view of an exemplary fixation screw andhex-shaped proximal extension implanted in the defect with the exemplaryguide pin replaced and an exemplary measuring tool arranged thereon, ina surgical procedure consistent with one embodiment of the presentinvention;

[0062]FIG. 9b is a side partial cross-sectional view of the exemplaryfixation screw and hex-shaped proximal extension of FIG. 9a implanted inthe defect with the exemplary guide pin replaced and an exemplarymeasuring tool arranged thereon, in a surgical procedure consistent withone embodiment of the present invention;

[0063]FIG. 9c is a perspective view of an exemplary fixation screw andproximal extension, with the cover removed, in one embodiment of thepresent invention;

[0064]FIG. 10a is a sectional view of an exemplary fixation screw andhex-shaped proximal extension implanted in the defect, after removal ofthe hex-shaped proximal extension, with an exemplary pin and suturestrands placed therethrough, in a surgical procedure consistent with oneembodiment of the present invention;

[0065]FIG. 10b is a side partial cross-sectional view of the exemplaryfixation screw and hex-shaped proximal extension of FIG. 10a, implantedin the defect, with an exemplary pin and suture strands placedtherethrough, in a surgical procedure consistent with one embodiment ofthe present invention;

[0066]FIG. 11a is a sectional view of an exemplary fixation screwimplanted in the defect, with an exemplary pin and suture strands placedtherethrough, showing the implanted fixation screw with the implantbeing tensioned on the suture strands, in a surgical procedureconsistent with one embodiment of the present invention;

[0067]FIG. 11b is a partial cross-sectional view of the exemplaryfixation screw of FIG. 9a implanted in the defect, showing the implantpositioned in the interchondular notch, in a surgical procedureconsistent with one embodiment of the present invention;

[0068]FIG. 12 is a sectional view of an exemplary fixation screwimplanted in the defect, wherein, after placement of the implant andremoval of the suture strands, the implant is driven into place with animpactor and hammer, in a surgical procedure consistent with oneembodiment of the present invention;

[0069]FIG. 13 is a side cross-sectional view of an exemplary fixationscrew implanted in the defect, after placement of the implant, wherein,after removal of the impactor and hammer, cement is injected between theimplant and the bone, in a surgical procedure consistent with oneembodiment of the present invention;

[0070]FIG. 14a is a schematic representation of the two datum curvesused to define a patient-specific three-dimensional surface forconstruction of the articular or lower surface of an implant in oneembodiment of the present invention;

[0071]FIG. 14b is a top view of an exemplary hex-shaped proximalextension in one embodiment of the present invention;

[0072]FIG. 14c is a perspective view of the bone-contacting or uppersurface of an exemplary implant, in one embodiment of the presentinvention;

[0073]FIG. 15a is a perspective view of an exemplary compass instrument,in one embodiment of the present invention;

[0074]FIG. 15b is a perspective view of the distal offset arm of anexemplary compass instrument and cutting blade to be mounted thereon, inone embodiment of the present invention;

[0075]FIG. 15c is a perspective view of an exemplary driver, showing anexemplary implant on an exemplary tether element, in one embodiment ofthe present invention;

[0076]FIG. 15d is a perspective view of an exemplary driver, showing anexemplary implant tensioned on an exemplary tether element, in oneembodiment of the present invention;

[0077]FIG. 16 is a perspective view of an exemplary compass instrumentand cutting blade mounted on an exemplary guide pin, in one embodimentof the present invention;

[0078]FIG. 17a is a perspective view of another exemplary cutting blade,in one embodiment of the present invention;

[0079]FIG. 17b is a perspective view of an exemplary measuring probe, inone embodiment of the present invention;

[0080]FIG. 17c is a perspective view of an exemplary multi-faced blademounted in the distal offset arm of an exemplary compass instrument, inone embodiment of the present invention;

[0081]FIG. 18a is a perspective view of an exemplary site preparationand cutting device, in one embodiment of the present invention;

[0082]FIG. 18b is a cross sectional view of the exemplary sitepreparation and cutting device of FIG. 18a, in one embodiment of thepresent invention;

[0083]FIG. 18c is a perspective view of another exemplary sitepreparation and cutting device, in one embodiment of the presentinvention;

[0084]FIG. 18d is a side view of another exemplary site preparation andcutting device, in one embodiment of the present invention;

[0085]FIG. 18e is a perspective view of another exemplary sitepreparation and cutting device, in one embodiment of the presentinvention;

[0086]FIG. 19a is a sectional view of the upper surface of an exemplaryimplant, in one embodiment of the present invention;

[0087]FIG. 19b is a side view of a portion of the exemplary implant ofFIG. 19a, in one embodiment of the present invention;

[0088]FIG. 19c is a perspective view of the upper surface of theexemplary implant of FIG. 19a, in one embodiment of the presentinvention;

[0089]FIG. 19d is an exploded perspective view of another exemplaryimplant with taper lock ring, washer and suture, in one embodiment ofthe present invention;

[0090]FIG. 19e is a top perspective view of the exemplary implant ofFIG. 19d seated in the taper lock ring, in one embodiment of the presentinvention;

[0091]FIG. 19f is a bottom perspective view of the exemplary implant ofFIG. 19d seated in the taper lock ring, with washer and suture, disposedwithin an incision near the defect site, in one embodiment of thepresent invention;

[0092]FIG. 19g is a perspective view of the exemplary implant of FIG.19d seated in the taper lock ring, with washer and suture, wherein thesuture is threaded through an aperture at the distal end of a seatingtool, at a first point in time during the process of seating the implantinto the defect site, in one embodiment of the present invention;

[0093]FIG. 19h is another perspective view of the exemplary implant ofFIG. 19d seated in the taper lock ring, with washer and suture, whereinthe suture is threaded through an aperture at the distal end of aseating tool, at a second point in time during the process of seatingthe implant into the defect site, in one embodiment of the presentinvention;

[0094]FIG. 19i is another perspective view of the exemplary implant ofFIG. 19d seated in the taper lock ring, wherein the distal end of aseating tool is disposed onto the implant, at a third point in timeduring the process of seating the implant into the defect site, in oneembodiment of the present invention;

[0095]FIG. 20a is a perspective view of an exemplary inner recordingelement of an exemplary measuring device, in one embodiment of thepresent invention;

[0096]FIG. 20b is a perspective view of an exemplary outer markingelement of an exemplary measuring device, in one embodiment of thepresent invention;

[0097]FIG. 20c is a cross-sectional perspective view of an exemplarymeasuring device showing an exemplary inner recording element and anexemplary outer marking element, in one embodiment of the presentinvention;

[0098]FIG. 20d is an exploded perspective view of another exemplarymeasuring device, in one embodiment of the present invention;

[0099]FIG. 20e is a perspective view of the exemplary measuring deviceof FIG. 20d, illustrating an exemplary scroll alignment feature, in oneembodiment of the present invention;

[0100]FIGS. 20f and 20 g are side views of the exemplary measuringdevice of FIG. 20d illustrating the translational motion of the handlewith respect to the tip of the device, in one embodiment of the presentinvention;

[0101]FIG. 20h is a perspective view of the distal end of the exemplarymeasuring device of FIG. 20d, in one embodiment of the presentinvention;

[0102]FIG. 20i is a perspective view of the distal end of the exemplarymeasuring device of FIG. 20d with outer element, disposed upon the innerelement engaging a mating feature of the screw, in one embodiment of thepresent invention;

[0103]FIG. 21 is a perspective view of an exemplary unitary implant, inone embodiment of the present invention;

[0104]FIG. 22 is a perspective view of a defect site with a keyedaperture for receiving the exemplary unitary implant of FIG. 21, in oneembodiment of the present invention;

[0105]FIG. 23 is a perspective view of an exemplary composite implant,in one embodiment of the present invention;

[0106]FIG. 24 is a perspective view of another exemplary compositeimplant, in one embodiment of the present invention;

[0107]FIG. 25 is a perspective view of an exemplary implant illustratingthe geometry of said implant for use in an algorithm for establishingminimum implant thickness, in one embodiment of the invention;

[0108]FIG. 26 is a perspective view of an exemplary implant illustratingthe geometry of said implant for use in an algorithm for establishingminimum implant thickness, in one embodiment of the invention;

[0109]FIG. 27a is a perspective view of an exemplary drill guide devicein an exemplary generic bone implant embodiment of the presentinvention;

[0110]FIG. 27b is a perspective view of another exemplary drill guidedevice in an exemplary generic bone implant embodiment of the presentinvention;

[0111]FIG. 28a is a top sectional view of the anterior-posterior planeof an articulating surface in an exemplary generic bone implantembodiment of the present invention;

[0112]FIG. 28b is a side sectional view of the medial-lateral plane ofan articulating surface in an exemplary generic bone implant embodimentof the present invention;

[0113]FIG. 29 is a perspective view of the use of an exemplary drillguide in an exemplary generic bone implant embodiment of the presentinvention, as the drill guide is brought up to a lesion site of thearticulating surface;

[0114]FIG. 30 is a perspective view of the use of an exemplary drillguide in an exemplary generic bone implant embodiment of the presentinvention, as the drill guide is seated into position and a guide pin isdriven through the drill guide;

[0115]FIG. 31 is a perspective view of the articulating surface in anexemplary generic bone implant embodiment of the present invention, as abone drill is passed over the guide pin to create a pilot hole for thescrew;

[0116]FIG. 32 is a cross-sectional view of the articulating surface inan exemplary generic bone implant embodiment of the present invention,as the screw is driven into the pilot hole with a cap positioned intothe screw;

[0117]FIG. 33 is a cross-sectional view of the articulating surface inan exemplary generic bone implant embodiment of the present invention,as the cap is removed and a rod is inserted into the screw, and theguide is positioned back over the rod and returned to its position incontact with the articular surface;

[0118]FIG. 34 is a side perspective view of the articulating surface inan exemplary generic bone implant embodiment of the present invention,as the guide is used to take a depth measurement needed for implantgeometry;

[0119]FIG. 35 is a top perspective view of the lower surface of anexemplary implant in an exemplary generic bone implant embodiment of thepresent invention;

[0120]FIG. 36 is a side perspective view of an exemplary implant in anexemplary generic bone implant embodiment of the present invention;

[0121]FIG. 37 is a side perspective view of another exemplary implant inan exemplary generic bone implant embodiment of the present invention;

[0122]FIG. 38 is a perspective view of the articulating surface in anexemplary generic bone implant embodiment of the present invention, asthe implant site is reamed with a cutting/reaming tool in preparationfor receiving an implant;

[0123]FIG. 39 is a top perspective view of an alternative exemplarycutting/reaming tool in an exemplary generic bone implant embodiment ofthe present invention,

[0124]FIG. 40 is a side perspective view of an exemplary cleaning toolfor cleaning the female taper of the screw prior to delivery of theimplant, in an exemplary generic bone implant embodiment of the presentinvention;

[0125]FIG. 41 is a side perspective view of an exemplary suction toolfor holding and delivering the implant, in an exemplary generic boneimplant embodiment of the present invention;

[0126]FIG. 42 is a side perspective view of an exemplary suction toolholding an implant in place, in an exemplary generic bone implantembodiment of the present invention;

[0127]FIG. 43 is a side cross-sectional view of an exemplary suctiontool holding an implant in place, with an implant in place, in anexemplary generic bone implant embodiment of the present invention;

[0128]FIG. 44 is a top perspective view of the articulating surface inan exemplary generic bone implant embodiment of the present invention,with the implant driven into its final position;

[0129]FIG. 45 is a side perspective view of an exemplaryremoval/revision tool in an exemplary generic bone implant embodiment ofthe present invention;

[0130]FIG. 46 is a side perspective view of an exemplaryremoval/revision tool, with an implant in place, in an exemplary genericbone implant embodiment of the present invention;

[0131]FIG. 47 illustrates an exemplary alternatively-keyed embodiment ofthe screw and the exemplary alternatively-keyed implant to which it isadapted to mate, in an exemplary embodiment of the present invention;

[0132]FIG. 48 illustrates a side cross-sectional view of an exemplaryalternatively-keyed embodiment of the screw, in an exemplary embodimentof the present invention;

[0133]FIG. 49 illustrates a side perspective view of the articularsurface of a lesion site and an exemplary biaxial measuring tool fordeveloping an axis normal to the articular surface, in one embodiment ofthe present invention

[0134]FIG. 50 illustrates another side perspective view of the articularsurface of a lesion site and an exemplary biaxial measuring tool fordeveloping an axis normal to the articular surface, in one embodiment ofthe present invention;

[0135]FIG. 51 illustrates a side exploded view of an exemplary biaxialmeasuring tool, in one embodiment of the present invention;

[0136]FIG. 52 illustrates a top perspective view of the distal end of anexemplary biaxial measuring tool in a first position, in one embodimentof the present invention;

[0137]FIG. 53 illustrates a top perspective view of the distal end of anexemplary biaxial measuring tool in a second position, in one embodimentof the present invention;

[0138]FIG. 54 illustrates an exemplary digital measuring system in oneembodiment of the present invention;

[0139]FIG. 55 illustrates an exploded perspective view of an exemplaryhandpiece in an exemplary digital measuring system in one embodiment ofthe present invention;

[0140]FIG. 55a illustrates a top perspective cutaway view of anexemplary printed linear index strip passing through an exemplary linearhead for reading, in an exemplary handpiece in an exemplary digitalmeasuring system in one embodiment of the present invention;

[0141]FIG. 55b illustrates a top perspective cutaway view of anexemplary printed rotary index strip passing through an exemplary rotaryhead for reading, in an exemplary handpiece in an exemplary digitalmeasuring system in one embodiment of the present invention;

[0142]FIG. 55c illustrates an exemplary linear index strip in anexemplary handpiece in an exemplary digital measuring system in oneembodiment of the present invention;

[0143]FIG. 55d illustrates an exemplary rotary index strip in anexemplary handpiece in an exemplary digital measuring system in oneembodiment of the present invention;

[0144]FIG. 56a illustrates a side perspective view of an exemplaryhandpiece with the probe assembly removed, in an exemplary digitalmeasuring system in one embodiment of the present invention;

[0145]FIG. 56b illustrates a side perspective view of an exemplaryhandpiece, including the probe assembly, in an exemplary digitalmeasuring system in one embodiment of the present invention;

[0146]FIG. 57 illustrates a top perspective view of an assembledexemplary handpiece, in an exemplary digital measuring system in oneembodiment of the present invention;

[0147]FIG. 58 illustrates a side perspective view of an assembledexemplary handpiece, in an exemplary digital measuring system in oneembodiment of the present invention;

[0148]FIG. 59 illustrates a top cross-sectional view of an assembledexemplary handpiece, in an exemplary digital measuring system in oneembodiment of the present invention;

[0149]FIG. 60 illustrates a side cross-sectional view of an assembledexemplary handpiece, in an exemplary digital measuring system in oneembodiment of the present invention; and

[0150]FIG. 61 illustrates a side cutaway perspective view of anexemplary base unit, in an exemplary digital measuring system in oneembodiment of the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0151] As an overview, FIG. 1 shows a surgically implanted articularjoint surface repair system consistent with the present invention. Asshown, the assembled fixation device includes fixation screw 10, implant40, and anchoring pin 5, implanted in the defect in the medial femoralchondral surface 55 of knee 50. Implant 40 is configured so that bearingor bottom surface 41 of the implant reproduces the anatomic contours ofthe surrounding articular surface of the knee 50.

[0152] As illustrated in FIGS. 2a, b and 3 a, fixation screw 10comprises threads 12 running the length of the screw from tapered distaltip 11 to hex-shaped drive 15. In the embodiment shown, the screwincludes a tapered distal end 11, and aggressive distal threads 12, sothat, as screw 10 is driven into the subchondral bone 100 (as shown inFIG. 7a) the screw dilates open and radially compress the subchondralbone, increasing its local density and thereby increasing the fixationstrength of the screw. The screw 10 may taper down to the distal end 11,and the diameter of the screw may become greater and more uniform at thecenter thereof, so that adjustment of the depth of the screw 10 withrespect to the subchondral bone 100 does not significantly furtherincrease or decrease the compression of the subchondral bone.

[0153] One or more milled slots 13 run the length of the uniformdiameter portion of the screw 10. Slots 13 ensure that as healing ortissue in-growth begins, migrational or rotational movement of the screwis inhibited. The screw 10 is configured to be driven by a female orsocket type driver 2 as shown in FIG. 7b, which engages a hex-shapeddrive 15 located toward the proximal end 17 of the screw. A cylindricalproximal extension 14 (which may, alternatively, be a recess 303 whichmates with a plug or other protrusion on the implant surface, as shownin FIG. 8c) extends from hex-shaped drive 15, which eventually serves asa fixation element for surface prosthetic implant 40. Through hole 16runs through the central axis of the screw. Hex-shaped cover 30 (whichmay, alternatively, be a plug 301, for mating with a fixation element302 having a recess, as shown, e.g., in FIGS. 3b, 8 c, and 9 c, anddescribed in the following paragraph) is configured to engage thecylindrical proximal extension 14 of the screw 10 to prevent exposure ofthe cylindrical extension from inadvertent contact or damage. Thehex-shaped cover 30 is finished with a radiused proximal end 31 thatassists in the visual determination of the correct depth setting of thescrew. Through hole 32 in the hex-shaped cover 30 corresponds withthrough hole 16 in the fixation screw 10.

[0154] Alternatively, as shown in FIGS. 3b, 8 c, and 9 c, thefemale-shaped cover may instead be a plug 301 having a male-shapedmating component 305, for mating with a fixation element 302 of a screw10′ having a recess 303. Additionally, the shape of the cover and plug,or other recessed, protruding, or mating components may be other thanhexagonal, and those in the art will recognize that one of any number ofshapes or configurations for such components may be employed in a deviceor method consistent with the invention.

[0155] Also, while many of the components described herein arecannulated, having guide apertures, through holes, and/or central luminaalong their length, for disposing such components about a guide rod forproper location of the components with respect to the articular surface,it should be recognized that a suture 313 or other flexible element, orother guide feature may be used in place of a guide rod, or a guide rodor wire may be eliminated altogether from one or more steps consistentwith the invention described herein. As shown in FIG. 8c, the suture 313may be fixedly or removably attached to the plug 301.

[0156] As shown in FIGS. 4a, 4 b and 4 c, implant 40 comprises lowerbearing surface 41, top surface 42 and protrusion 45 located centrallyon the bottom surface. As the top surface 42 of the implant 40 is not abearing surface, and instead is fixed into subchondral bone 100, aseries of stepped machine cuts 43 following the contours of the defectare created. By creating stepped machine cuts 43 a contoured contactsurface matching the defect in the subchondral bone 100 is created. Thiscontact surface results in an increased surface area that should enhanceresistance to loosening of the implant 40 via rotational ortranslational loading. In the illustrated embodiment, the stepped cutsare shown as square cross-section cuts, but the cuts may be circular,triangular, or another configuration.

[0157] In order to secure the implant 40 to the fixation screw 10,precision taper 44 is machined into or onto a protrusion 45 on the topsurface 42 of the implant. The precision taper 44 is configured toengage the cylindrical proximal extension 14 of the screw 10, once thehex-shaped cover 30 has been removed therefrom. Taper 44 may be matedwith extension 14 so that a friction fit is provided between thesesurfaces. The assembled fixation device is shown in FIGS. 5a and 5 b.Alternatively, other engagement mechanisms such as snap-fits,press-fits, threads, or coupling elements, for example, may also beused. In one embodiment, leading pin 47 arranged on the protrusion 45assists penetration into subchondral bone. Also, in one embodiment,guide aperture 46 passes through the top 42 and bottom 41 surfaces ofthe implant 40, just slightly off center of the reference axis 20A.Alternatively, guide aperture 46 may be located in the center of theimplant 40 and corresponds to through hole 16 running through thecentral lumen in the fixation screw 10. Bone cement may be injectedthrough guide aperture 46 on the surface of the implant 40 and throughhole 16 in the fixation screw 10, to enhance the contact surface betweenthe device and the subchondral bone. In one embodiment, the implant isconstructed of cobalt chromium, although other materials may be used,including implantable plastics. Additionally, biologically activecoatings or surface treatments (e.g., to enhance bone ingrowth orimprove wear properties) may be utilized or combined as laminates,particularly with respect to the bearing surfaces and bone contactingsurfaces. Further exemplary materials that may be used in fabricating animplant consistent with the invention are described hereinbelow.

[0158] As shown in FIG. 3b, it is noted that precision taper 44 may be amale-shaped component 304 instead of the above-described femalecomponent 44. In this configuration, the male-shaped component 304 ofthe implant 40′ is configured for mating with a fixation element 302 ofthe screw 10′ having a recess 303 adapted to receive the male-shapedcomponent 304.

[0159] By way of example, FIGS. 6a-13 depict one exemplary joint surfacemethodology of the present invention. FIG. 6a shows a focal defect 1 ofthe articular surface 55 of the femoral chondyle bone of the knee 50.This defect is identified by arthroscope 25 inserted in the area of thedefect 1 during a diagnostic arthroscopy or surgical arthroscopy. Thedisclosed surgical intervention begins by drilling a guide pin 20defining reference axis 20A into the central portion of the defect 1 viaan incision 200 typical of arthroscopic procedures. Placement of thispin may be done using visual, freehand techniques, or may be locatedcentrally by using outer element 71 of a measuring tool 70 (as shown inFIGS. 9a and 9 b), or other aiming device or technique, to define acenter. This reference axis 20A serves to establish a working axislocated central to the defect 1 for the procedures that follow, andarthroscope 25 may be used to view the joint for purposes ofestablishing a reference axis 20A generally perpendicular to andbisecting the existing articular surface 55 defined by radii 60 and 61,as shown in FIG. 8b. Referring to FIG. 7a, 7 b, 8 a and 8 b, fixationscrew 10 and hex-shaped cover 30 are driven into the defect 1 in thesubchondral bone 100 by socket-type driver 2 mounted over (i.e., about)guide pin 20 located on reference axis 20A. Under arthroscopic view, thedepth of fixation screw 10 may be adjusted by driver 2 so that thebottom of the radiused surface 31 of the hex-shaped cover 30 ispositioned tangent to the radii 60 and 61 that define the existingarticular surface 55. The guide pin 20 is removed and the knee 50 isarticulated through its range of motion to ensure that the height of theradiused surface 31 of the hex-shaped cover 30 is proper, since theprosthetic surface 41 of the implant 40 is created also to be tangent tothis radiused surface 31. The depth positioning of the radiused surface31 of the hex-shaped cover 30 establishes a point of origin or areference point for all future measuring and machining operations.Arthroscopic examination may be carried out from multiple arthroscopicviews to confirm positioning.

[0160] A drill mechanism 306, as illustrated in FIG. 6b, may be used tobore a pilot hole for receiving a fixation screw 10 (as shown, e.g., inFIGS. 2a, 2 b and 3 a). As shown, the drill may have a shank portion 307and a bit portion 308. The bit portion 308 may include a spiral orparabolic fluted tip 309 having proximal 310, medial 311, and distal 312portions. The root diameter at the medial portion 311 is substantiallyequal to the diameter of the fixation screw 10, and the diameterdecreases as the distal portion 312 tapers away from the shank 307. Theproximal portion 310 of the bit 308 may be used as a visual indicatorduring drilling, to determine the point at which the proper bore depthhas been attained. The drill mechanism may have a central lumen (notshown) having a diameter slightly greater than the diameter of the guidepin 20 (as illustrated in FIG. 6a) running along its length, so that,with the guide pin 20 in place, the drill 306 may be disposed about theguide pin 20 during drilling to ensure proper location of the pilot holewith respect to the articular surface 55. Alternatively, a self-drillingor self-tapping screw, may be used, as those skilled in the art willrecognize.

[0161] For surface preparation and accurate measurement of the implantsite and the subsequent sizing of the implant, instrument 120 isprovided. The compass instrument 120 may be configured to serve as amounting tool for a number of functional blades or tips and when locatedabout the axis 20A, via guide rod 20, may be used for measuring andcutting operations. In the embodiment shown in FIG. 15a, compassinstrument 120 includes handle 110, a cannulated shaft 111 that extendsthrough the handle, and a cannulated distal offset arm 112. Theinstrument may be rigid in construction and may be a durable reusableand resterilizable instrument. The distal offset arm 112 is configuredso that it can be introduced into a site through an incision 200 typicalof an arthroscopic procedure. Once the distal offset arm 112 has fullypenetrated the incision and enters the site, shaft 111 can be angularlyrepositioned so that it becomes more coaxial to the reference axis 20Aand advanced in-line with the reference axis 20A towards the implanttarget site. While performing this maneuver to position the compassinstrument 120, the guide pin 20 should be removed from its position inthe defect 1. When compass 120 is in its proper position at or near theimplant target site, the guide pin 20 is delivered through theinstrument cannulation 113, re-establishing the working (reference) axis20A used to define the implant geometry.

[0162] Referring to FIG. 15b, within offset arm 112 is a slotted surface114 for engaging a series of cutting blades 121, boring blades 124, ormeasuring probes 122. The slots 115 are configured so that said seriesof cutting blades 121, boring blades 124 (FIG. 17c), measuring probes122, 123 (FIGS. 17a, 17 b), or like elements may be partiallyconstrained or fixed in position such that they may be adjusted linearlyalong the length of the slotted surface 114 over a defined distance oftravel. Intersecting the plane of travel defined by slotted surface 114and slots 115, is the cannulation 113.

[0163] As illustrated in FIG. 16, when fitted with a cutting blade 121,and with the guide pin 20 advanced through the shaft 113 of instrument120, so that the guide pin passes through a closely sized hole 116 inthe cutting blade, the blade's position becomes fully constrained. Whenconstrained in this fashion, a fixed length from the rotational orreference axis 20A to the cutting surface 117 of cutting blade 121 isestablished. This defines the radius that is effected as the instrument120 is rotated around the guide pin 20, and corresponds to the overalldiameter of the implant 40 that is delivered to the fully prepared site.The cutting blade 121 is used to circumscribe and cleanly cut thesurrounding articular cartilage.

[0164] In an alternative embodiment, as shown in FIGS., 17 a and 17 b,blade 123 and measuring probe 122, respectively, may have multiple holes118 that defines that probe/blade's functional diameter. In addition,the blades may be specifically configured so that staged or sequentialcuts of varying depths and diameters can be performed within theprocedure. Also, such a blade can be configured by providing a readablescale 119 corresponding to the hole 118 pattern, so that the surgeon maydetermine and set the appropriate diameter as needed by positioning theguide pin 20 in the corresponding hole. As the readable scale 119 may belocated on the blade 123 with respect to the blade's cutting surface117, a high degree of positional accuracy may be achieved as the scalemay be defined specifically for each type of blade. This approachcreates an inexpensive means of providing sharp blades of varyingdiameters and varying blade types without a large inventory of size- andtype-specific blades. Referring to FIG. 17b, rounded tip 109 ofmeasuring probe 122 can be used to determine the appropriate diameterand can be similarly sized and secured in the compass instrument 120.The tip 109 may be rounded to prevent marring of the articular surface.FIG. 17c shows a boring bit or bone cutting blade 124 with multiplecutting surfaces 107 and 108 configured in this fashion.

[0165] Turning now to FIGS. 9a and 9 b, with the guide pin 20 replaced,a measuring tool 70 is inserted so that the reference axis 20A isutilized. A central element of the measuring tool 70 is a post 75 thatis static, establishes the axial location of the point of origin 80, andmates with a rotational location feature within the screw 14. Byrotating the outer arm or outrigger 71 of the measuring tool 70 relativeto the static post 75 while also maintaining contact with the articularsurface 55, an axial displacement or Z dimension can be establishedrelative to the point of origin 80 for any point along the sweep of theoutrigger. Each such Z dimension may be recorded in real time withconventional dial gauge indicators 72 or with a digital recordingdevice, such as disclosed in U.S. Pat. No. 5,771,310 to Vannah, or byusing other known marking techniques. Although numerous points may betaken, ideally a minimum number of points are taken to define accuratelythe target articular surface. In other embodiments, multiple outriggersthat embody different diameters or an adjustable outrigger may be usedto map larger defects, and also to determine the final diameter of theprosthetic surface that fits within the defect. It is noted that themeasuring tool may comprise a spring or other tensioning device (notshown), for urging the outrigger distally with respect to the handle ofthe tool. In this aspect, the outrigger is manually pressed against thearticular cartilage, so as to maximally compress the articular cartilageupon recording data points, so that the data points taken are of amaximally “loaded” or “compressed” dimension.

[0166]FIGS. 20a, 20 b and 20 c show an alternative measuring and mappingdevice 210 for obtaining the articular surface dimension, comprisinghousing 217 and a recording element 218. As shown in FIG. 20a, recordingelement 218 includes upper portion 219, flange 222 and calibrated lowerportion 220. Key-shaped surface 221 located at distal end 225 ofrecording element 218 is configured to engage a reciprocal key-shapedsurface in the proximal extension 14 of fixation screw 10, or, forexample, a key shaped cover arranged on the proximal end of the screw(not shown). The upper portion 219 of recording element 218 may beconstructed of a relatively soft or other deformable material that canbe marked with patient data. Cannulated shaft 223 runs through thecentral lumen of the recording element 218. As shown in FIG. 20b,housing 217 includes a marking mechanism 224 located on the upperportion 226 of the housing, at or within window or aperture 230. Anindexing indicator 228 is located on the lower portion 227 of thehousing 217, at window or opening 229.

[0167] Turning to FIG. 20c, recording element 218 is inserted in housing217 of measuring and mapping device 210, so that the distal end 225 ofrecording element 218 appears through opening 232. Tensioning means (notshown) in the device 210, enables recording element 218 to movelongitudinally within housing 218. With the guide pin 20 replaced, themeasuring device 210 is inserted on the guide pin on reference axis 20Aso that key-shaped surface 221 engages the corresponding keyed surfaceof the screw and is maintained in static position thereby. Thesekey-shaped surfaces establish the rotational position of the articularsurface points to be mapped relative to the screw. During the measuringand mapping procedure, the surgeon rotates housing 217 and outer arm oroutrigger 231 located at the distal end 235 of housing. By depressingmarking mechanism 224, a series of depressions or marked points 240 isestablished in the relatively soft surface of the upper portion 219 ofthe recording element 218, which deforms at these marked points so thatthey can be utilized as patient data. Indexing indicator 228 andcalibrated lower portion 220 of recording element 217 allow forcontrolled rotational movement between housing 217 and recording element218. In this way, the rotational position of the mapped articularsurface points 235 relative to the screw 10 as appreciated by outer armof outrigger 231, is translated to the implant geometry as a feature sothat the accurate rotational location of the implant 40 relative to thescrew 10 is maintained.

[0168] For example, as shown in FIGS. 8b and 9 b, to accuratelyreproduce the two radii 60 and 61 that locally define the articularsurface 55, four points, 81 a and 81 b, and 82 a and 8 b, and the pointof origin 80 are recorded. As any three points in a single plane definea curve, by recording points 81 a and 81 b and the point of origin 80,radius 60 defining the medial-lateral aspect 68 of the chondyle can bedetermined. By recording points 82 a and 8 b and the point of origin 80,the radius 61 defining the anterior-posterior aspect 69 of the chondylecan be determined. In the example provided, in order to maintain therelationship between these two defined radii, 60 and 61, the measuringtool 70 is constructed so that it can be accurately indexed from a fixedstarting point along 90 degree intervals to capture or map said fourpoints 81 a, 81 b, 82 a and 8 b, over the course of its revolution.

[0169] Locating surfaces or features created on the radius cover 30, oralong some length of the fixation screw 10, hex-shaped drive surface ofthe screw 14 or on the cylindrical proximal extension (or recess) of thescrew 14, correlate to some surface or feature on the measuring tool 70and allow the measurement of the rotational position of the fourmeasured points 81 a, 81 b, 82 and 8 b, about the reference axis 20Awith respect to said locating surfaces. This data becomes important inconfiguring the implant 40 with respect to the fixation screw 10 so thatthe proper orientation of said measured points to fabricated geometry ismaintained. Of course, such measuring tool can be configured to measureany number of points at any interval desired.

[0170] While the measurements are illustrated in FIGS. 9a and 9 b asbeing taken from the bottom of the radiused surface 31 of the hex-shapedcover 30 of the screw, the measurements may alternatively be taken fromthe top of the screw 10′ itself, as shown in FIG. 9c. As shown, in thisembodiment, a key 315 or other alignment feature may be provided, toindicate the starting point for taking measurements. In thisconfiguration, the measuring tool used, as well as the implantmanufactured, both have a mating feature matching the key 315, forproperly locating the starting point of the measurements taken andthereby subsequently properly aligning the implant with respect to thedefect.

[0171] Other embodiments of measuring and recording tools are possible.One such embodiment of a measuring and recording tool 210′ is shown inFIGS. 20d- 20 i. As shown, measuring tool 210′ comprises a handle 316,outer shaft 333, inner shaft 330, scroll 317, a tactile feedback portion318, ring 320 having a button 321 in communication with a sharp markingpoint 326 thereunder, a rotating portion 322 having a rotational lock323 which prevents rotation of the rotating portion 322 when engaged,and an outrigger portion 324. The handle 316 remains fixed duringrotation and does not move while the tool 210′ is used for measuring.Instead, the rotating portion 322 is rotated to a start position and therotational lock is engaged, securing the rotating portion 322 to thetactile feedback portion 318 and thereby preventing its rotation. Thescroll 317 is configured with a notch 325 or similar mating feature toalign with a corresponding mating feature (not shown) of the handle 316,such that the scroll can only align at one rotational point, at 0degrees, with respect to the handle 316 upon loading into the tool 210′,e.g., by “snapping” into place. The sharp marking point 326 locatedinside the ring 320 under the sharp marking point 326, marks a point ofdepression into the scroll 317 while first button 321 is beingdepressed. Instead of marking by making depressions on a scroll orspool, marking could alternatively be made upon nearly any surface,e.g., using ink to record on a paper spool, or by digital means.

[0172] As shown in FIGS. 20f and 20 g, outer shaft 333, which is fixedlycoupled to rotating portion 322, outrigger 324 and ring 320, is freelyrotatably disposed about inner shaft 330 and slidably disposed aboutinner shaft 330 within a range bounded by points 334 and 337. In FIG.20f, the outrigger 324 is retracted, and outer shaft 333 is located at aposition of origin along a z-axis parallel to the inner 330 and outer333 shafts, such that the proximal end of the ring 320 is located atposition 335. In FIG. 20g, the outrigger 324 is extended, and outershaft 333 is located at a position 0.250 in. (0.64 cm.) from the originof the z-axis parallel to the inner 330 and outer 333 shafts, such thatthe proximal end of the ring 320 is located at position 335′. The motionof the sliding of the outer shaft 333 about inner shaft 330 duringmarking is translated via the outer shaft 333, rotating portion 322 andring 320 (including marking button 321 and marking point 326) to alocation along the scroll 317. Thus, as the user rotates outrigger 324by rotation of rotating portion 322, the outrigger moves along thearticular surface proximally or distally with respect to the innershaft, and the displacement of the outrigger 324 along a z-axis parallelto the inner 330 and outer 333 shafts may be marked on the scroll 317 bydepression of the button 323 at various points along the rotation of theoutrigger 324. The tactile feedback portion 318 has a series ofdepressions 319 or other tactile feedback means, e.g. spring ballplungers which engage in indentations (not shown) in the inner shaft330, spaced at 90 degrees from one another, so that when the rotationallock 323 is engaged as rotating portion 322 is being rotated, the userfeels a “click” or other tactile feedback to indicate to the user therotational location of the rotating portion 322 at 90 degree intervalswith respect to the handle 316, i.e., at 90 degrees, 180 degrees, 270degrees, and 0 (or 360) degrees, for purposes of marking at thosepoints. It is further noted that the starting point for marking may ormay not be selected independent of the 90-degree rotational points, andthat the rotating portion 322 may or may not be is configured so that itis not tied to the 90-degree indexing until the scroll lock 323 isengaged.

[0173] As shown in FIGS. 20e, 20 h and 20 i, a keyed mating feature 331may be disposed at the distal end of the inner shaft 330 with respect tothe outrigger portion, for mating with a key feature 315 on the screw10′ (as shown in FIGS. 9c and 20 i), so as to locate properly thestarting point of the measurements taken with respect to the screw, andthe scroll 317. FIG. 20h illustrates a more detailed view of the distalend of the marking tool 210′, with outer shaft 333, inner shaft 330 withkeyed mating feature 331, and outrigger 324 with rounded end 338, whichtravels along the path of circle 339.

[0174]FIG. 20i illustrates the measuring tool 210′, with the keyedmating feature 331 inserted into the recessed portion 303 of the screw10′ at its fixation element 302.

[0175] Referring now to FIG. 14a, data recorded during the mappingprocedure described above can then be entered into a known parametricengineering design software or similar algorithm, as four values, 85 a,85 b, 85 c, and 85 d, corresponding to the four measured points, 81 a,81 b, 82 a and 8 b, with the origin 80 defining a reference plane. Thesefour values 85 a, 85 b, 85 c and 85 d, are represented by line elementsthat are geometrically constrained to lie upon a circle 90, whichrepresents the diameter of the measuring tool 70. These line elementsare also constrained to lie within planes that are perpendicular to oneanother. Of course, more than four points may be taken and used to mapthe articular surface, e.g., 8 points; however, a minimum of four pointsshould be taken, so that two intersecting datum curves may be definedfor purposes of mapping.

[0176] Datum curves 86 and 87, representing the medial-lateral (“ML”)and anterior-posterior (“AP”) curves, are constructed by connecting theend points of the line elements 81 a and 81 b, and 82 a and 8 b and thepoint of origin 80, which is common to both curves. These two datumcurves 86 and 87 can be used to construct the articular or bottomsurface 41 of the prosthetic implant 40. By sweeping datum curve 87along a path defined by datum curve 86, a three dimensional surface isnow defined.

[0177] By constructing this series of geometric relationships in a knownparametric engineering model, patient-specific geometry can be input asvalues and the model algorithm can be run to reproduce the anatomiccontours mapped in the patients within only a few moments. As a process,this generic model is the starting point for all patient treatments.Sterile pins, screws, and measuring devices that are allnon-patient-specific may be stocked in the hospital and ready to usewhenever an appropriate defect is diagnosed. Patient-specific data maybe transmitted from the surgeon to the fabricating facility via aninterface to the Internet or other network. Data input into theinterface may be read directly into the generic parametric model toproduce a viewable and even mappable patient-specific parametric modelwithin moments. Confirmation by the surgeon could initiate a work orderfor the production of the patient specific device. Existing technologyallows the parametric model to generate toolpaths and programming, e.g.,to a CAD/CAM system comprising appropriate hardware and/or softwarecoupled to appropriate data-driven tools, to fabricate the implant.

[0178] Defining two additional datum curves 88 and 89, at offsetdistances from datum curves 86 and 87, is performed to define the top ornon-bearing surface 42 of the implant 40. This top surface 42 should beclosely matched to the bearing surface geometry to be implanted withouthaving to remove an excessive quantity of bone from the chondralsurface.

[0179] Referring to FIGS. 14c and 19 c, implant geometry may be definedwhereby the top or bone contacting surface 42 of the implant 40 exhibitsan axial symmetry. The central axis AA passes through the point oforigin 80 of the implant 40 and when the implant is positioned at thetarget site, aligns with the original reference axis 20A as defined bythe guide pin 20 and fixation screw 10. The central axis AA can then beused to define the preparation tools so that the bone contactingsurfaces 42 of the implant 40 and the preparation tools can be matchedin both configuration and dimension to create a mating fit between thesurface of the prepared target site and the bone contacting surfaces 42of the implant. For example, if the preparation tools can be fabricatedusing some of the same dimensions obtained during the articular surfacemapping procedure, the implant geometry and corresponding preparationtool geometry can be mated and optimized so that a minimum verticalthickness of the implant as well as a minimum depth of bone removal isrequired. This may be advantageous in ensuring good long term clinicalresults with the implant, as poor quality of fit between bone surfacesand bone-contacting surfaces of traditional orthopedic prostheticdevices has been noted to contribute to early clinical failures.

[0180] For example, as shown in FIGS. 14c and 19 c the top or bonecontacting surface 42 of the implant 40, a series of radial cuts 198 maycreate surfaces that increase resistance of the implant to rotationalforces. These features may be located at the outer diameter 190 of theimplant 40 to increase their effectiveness. Additional contact surfacesmay also be created by one or more protrusions 195 located on the bottom42 of the implant. Similarly, surface treatments known in the field oforthopedic devices, such as porous and/or osteoconductive coatings, maybe utilized on surface 42.

[0181] As shown in FIG. 19b, outer diameter 190 may include a slightoutward taper or protrusion 197 along the diametrical surface to enhanceload bearing or load transfer properties of the implant to surroundingbone. This feature may also increase the fixation strength of theimplant. A fillet 199 (as shown in FIG. 19a) that runs around theimplant at the intersection of the diametrical surface 190 and thebearing surface 41 is also useful in providing a smooth transitionbetween the host articular cartilage and the implant surface.

[0182] However, if a greater depth of implant is needed as a result ofthe defect appearance the offset curves 88 and 89 (as shown in FIG. 14a)can be extended to increase the overall thickness of the implant 40 orthe offset curves may be eliminated entirely so that the contouredsurface is backed by a revolved geometry that is symmetrical toreference axis 20A. Turning to FIG. 19c, where the ML curve and AP curve(defined by the obtained measurements) are not axially symmetrical, thethickness of the implant 40 requires adjustment. At the same time, anunnecessarily thick implant requires a greater amount of bone to beremoved at the target site. Therefore, the thickness of the implant maybe determined by taking the largest obtained measurement and adding aminimal offset amount 208. (The implant is thinnest at the highest pointon the ML curve.) This can be similarly accomplished by adjusting theangle A (FIG. 19a) of the bone-contacting surface 42 of the implant 40and a corresponding angle of the preparation tool. This also allows fora correction of the implant geometry, to compensate for anynon-perpendicular placement of the guide pin with respect to thearticular surface.

[0183] With reference now to FIGS. 25 and 26, an exemplary algorithmconsistent with the invention establishes the minimum thickness of animplant necessary to include all patient data points, receiving as inputall of the points measured (typically, four) and identifying the largestvalue. One such exemplary algorithm is as follows (and as shown in FIGS.25 and 26): maxval= D6 if maxval < D11 maxval = D11 endif if maxval <D14 maxval = D14 endif D684 = maxval + .045

[0184] In the foregoing exemplary algorithm, a first data point D6 isinitially assigned as the maximum value (maxval). If . . . then typestatements are used to compare other data points (D11 and D14) tomaxval. If other data points are greater than maxval, the algorithmreassigns maxval to the new larger data point. LLMT represents theheight of the lower limit plane along the z-axis, and ULMT representsthe height of the upper limit plane along the z-axis. D684 is adimension that controls the ULMT plane, which is established in themodel as the upper surface of the implant. ULMT is positioned as maxvalplus an additional arbitrary and/or fixed material offset (0.045 in thiscase).

[0185]FIGS. 5c and 5 d illustrate an alternative embodiment of theimplant 40′, having a ML curve between data points 340 and 341 and an APcurve between data points 342 and 343, with male-shaped mating component304 and key-shaped portion 344 for engagement with a reciprocalkey-shaped surface in the proximal extension of a fixation screw,protrusions 345 (creating contact surfaces on the top 346 of the implant40′), radial cuts 347 located at the outer diameter 348 of the implant40′, and radius 349 (which may be formed, e.g. using an abrasive wheel)around the intersection of the outer diameter at point 341 and thesurface comprising the patient geometry.

[0186] Referring to FIGS. 18a and 18 b, bone cutting or scoringinstrument 250 includes a handle (not shown), a cannulated shaft 111that extends through the handle, and offset arm 140 housing adjustableblades 141. In the embodiment shown, individual cutting blades 141 areattached to offset arm 140 either fixedly or removably, e.g. viathreaded portions 142, into threaded recesses 342 of the offset arm 140,although other attachment means may be used. With guide pin 20 advancedthrough shaft 113 positioned on the reference axis 20A, a fixed distancefrom the rotational or references axis 20A to each of the cutting orscoring blades 141 is established. These lengths define the radii thatare to be effected in the articular surface, as the scoring instrument250 is rotated around the guide pin 20, corresponding to the protrusions195 on the bone contacting surface 42 of the implant 40 creating amatching fit between the bone surfaces of the prepared target site andthe bone contacting surfaces of the implant.

[0187] In an alternative embodiment, as shown in FIG. 18c, cuttingblades are arranged on carrier 145, configured so that it can be mountedwithin the slotted surface 114 of offset arm 112, depicted in FIG. 17a.In another embodiment, as shown in FIG. 18d, cutting blades 141 can befixedly positioned on offset arm 140. Using the same dimensions obtainedduring articular surface mapping procedure, the cutting and scoringdevice 250 can be fabricated to prepare the articular surface tocorrespond to the implant geometry to optimize fit. In anotheralternative embodiment, as shown in FIG. 18e, a bone cutting instrument352 corresponds to the alternative embodiment of the implant 40′illustrated in FIGS. 5c and 5 d. Instrument 352 has a handle (notshown), a cannulated shaft 353 that extends through the handle andthrough the cannulation 355, offset arm 354 with blades 350 and 351corresponding to the protrusions 345 on the bone contacting surface 42of the implant 40 creating a matching fit between the bone surfaces ofthe prepared target site and the bone contacting surfaces 346 of theimplant 40′.

[0188] As shown in FIG. 14b, an angular dimension 95, relating somelocating surface or feature on the hex-shaped cover 30 or on thefixation screw 10, to the four points 81 a, 81 b, 82 a and 8 b, may alsobe captured at the time of the initial procedure to assist inorientation of the implant 40 to the fixation screw 10. Guide aperture46 in implant 40 is located off the reference axis 20A and may serve asthe locating feature and/or as a suture passage way in the implantationprocedure. Alternatively, a surface or feature created on the implant40, may serve to reference or align to such locating surface on thehex-shaped cover 30 or the fixation screw 10.

[0189] Additional data can be taken at the time of the initialprocedure, e.g., for fabricating a non-circular implant. Additional datacurves can also be defined by measuring the offsets from the referenceaxis 20A and determining diameters at these offsets. The final implantgeometry, although measured using circular techniques, need not becircular.

[0190] Referring to FIGS. 10a and 10 b, following fabrication of theimplant 40, a second procedure is performed. If a cover 30 (or plug) isin place, it is removed, exposing proximal extension 14 (or recess) orsome other precision taper or engagement surface located at the proximalend 17 of the fixation screw 10 to which the implant 40 is to beaffixed. A pin having a distally mounted element or barb 5 is placedthrough through hole 16 running through the central lumen of thefixation screw 10 so that the distally mounted element 5 is secured intothe screw. The distally mounted element 5 carries one or more suturestrands 85 that now trail from the fixation screw 10. Alternatively, apin, braided cable, or flexible wire may also be used. However, suturesmay make passing the implant 40 through the incision 200 and subsequenthandling easier.

[0191] Turning to FIGS. 11a and 11 b, the sutures 85 are then threadedthrough guide aperture 46 of the implant 40 and a knot or bead 49 may becreated proximal to the implant, so that tensing one of the free runningsutures 85 helps to advance the implant 40 toward the proximal extension14 (or recess) of the fixation screw 10. Alternatively, the suturestrands 85 can be passed through the central lumen or shaft of a drivingrod or other instrument to aid in seating the implant 40, and positionedin the fixation screw 10 thereafter.

[0192] If necessary, the arthroscopic wound 200 is expanded slightly ineither a vertical or horizontal direction, so that the implant 40 may bepassed through. A polymeric sleeve (not shown) positioned over theimplant may prove helpful in passing the implant through the incision.As shown in FIG. 11b, based on the size of the implant 40, anatomy ofthe knee 50, and retraction of the knee, it may be necessary to positionthe implant in the interchondular notch 77 as a staging area prior tofinal placement. By continuing to manipulate and tension the suturestrands 85, the implant 40 can be brought coaxial to the proximalextension 14 of the fixation screw 10.

[0193] As shown in FIGS. 15c and 15 d, alternatively, driver 130includes handle 110, a cannulated shaft 111 that extends through thehandle and a cannulated seat portion 131 attached to the end of theshaft. Tether element 135, which may comprise sutures or wire, is passedthrough driver 130 and is threaded through implant 40 through guideaperture 46, connecting the implant to the driver toward seat portion131. The implant 40 and the driver 130 are then insertedarthroscopically through incision 200 to the target site. By tensioningtether element 135 at the end 136 of handle 110, the implant 40 is drawnback into seat portion 131 of driver 130. By maintaining tension ontether element 135, the implant 40 can then be controllably delivered tothe prepared target site. At least the inner surface of seat portion 131comprises a material that can be impacted to seat the implant 40 withoutdamaging the implant surface.

[0194] Referring to FIG. 12, once coaxial, the implant 40 can be alignedvia engagement of the proximal extension 14 on fixation screw 10 andprecisions taper 44 on the bottom surface 42 of the implant and anylocating feature, and driven into place with a plastic driving rod 91and mallet 95. A protrusion 92 of high strength material mounted at thedistal tip 93 of the driving rod 91 may be necessary to ensure that therod stays centered on the implant 40 during driving.

[0195] Finally, as shown in FIG. 13, through guide aperture 46 on theupper surface 41 of the implant 40, bone cement 300 may be injected toenhance the contact surface between the implant 40 and the subchondralbone 100. Vents, such as milled slots 13 in the fixation screw 10, andin the walls of the implant central protrusion may be desirable tofacilitate the flow of such materials.

[0196] Alternatively, guide aperture 46 in the implant 40 may bealtogether eliminated by using an alternative implant delivery system,as shown in FIGS. 19d through 19 i, corresponding to an implant similarto that shown in FIGS. 5c and 5 d. The alternative system comprises theimplant 40″ and a washer 361 for holding a suture 363, the washer 361being adapted to fit into a taper lock ring 360. The ring 360 has ataper lock portion 362 having a series of notches 365 along itsperimeter, creating flaps 372 that permit the taper lock portion 362 toflex somewhat. The taper lock portion 362 has a diameter graduallytapering from the middle to the proximal end 364 of the ring. The taperlock ring 360 may also have an alignment notch 386 or similar featurefor properly aligning the taper lock ring 360 with respect to key-shapedportion 344 of the implant 40″, which is to engage with a reciprocalkey-shaped surface in the proximal extension of a fixation screw, so asto seat properly the implant rotationally with respect to the defectsite when it is later seated thereon. A washer 361 is disposed betweenthe ring 360 and the implant 40″ and has two apertures 366 disposed in arecessed area 367 in the center of the washer. The suture 363 isthreaded through the two apertures 366 to form a suture loop 368, whichremains in the recessed area when the ends of the suture 363 are pulled,so as to keep the suture loop 368 below the top surface 369 of thewasher 361. The implant 40″ has a diameter at its center portion 370that is approximately equal to the inner diameter of the ring 360 at itstaper lock portion 362. Thus, when tension is applied to the ends of thesuture 363, the taper lock portion 362 of the ring 360 may flex outwardto receive slidably therein the implant 40″ and washer 361, whichsubsequently lock into the taper lock portion 362 of the ring, once thecenter portion 370 of the sides of the implant 40″ is seated within theproximal end 364 of the ring by friction fit, as shown in FIG. 19e. Itis noted that the center portion 370 of the sides of the implant 40″ tobe of a width permitting the implant and washer to travel slidablywithin the ring 360 to some degree.

[0197] As shown in FIG. 19f, a hex nut 373 may be integrally formed inthe center of the washer 361 on its bottom side 374, for mating with anappropriately configured tool for seating the implant 40″. As FIG. 19fillustrates, the implant 40″, along with washer 361, ring 360, andsutures 363, is pushed through the incision 200 at the defect site.Next, as shown in FIGS. 19g-19 i, illustrative of successive steps inthe process of seating the implant, a seating tool 380 may be used toseat the implant. Seating tool 380 comprises a shaft 385, a handle 381(which may have a through hole 382, if the same handle and/or shaft isused with interchangeable tips for performing various functions,although a through hole 382 is not integral to seating the implant), andtip 383 suitably configured to drive hex nut 373 (or other matingfeature) and having an aperture 384 through which the ends of the suture363 may be threaded. Once the tip 383 of the tool 380 is introduced intothe incision 200, the sutures 363 may be used as a guide for seating thetip 383 of the tool 380 onto the hex nut 373, which may be accomplishedby alternately pulling on each end of the suture 363 to toggle the tip383 of the tool 380 back and forth. Once the tip 383 of the tool 380 isseated onto the hex nut 373, the tool 380 may be rotated in eitherdirection to seat the implant assembly properly (comprising implant 40″,taper lock ring 360, and washer 361) at the defect site. This may beeffected by rotating tool 380 until alignment notch 386 andcorresponding key-shaped portion 344 of the implant 40″ are aligned withthe corresponding reciprocal key-shaped surface in the proximalextension of the fixation screw, whereby the implant should slide intoplace, thereby properly seating the implant rotationally with respect tothe defect site. As shown in FIG. 12 with respect to the prior describedembodiment, once properly seated, the implant 40″ can be driven intoplace with a plastic driving rod 91 and mallet 95, and as shown in FIG.13 with respect to the prior described embodiment, bone cement 300 mayalso be placed prior to the final seating of the implant 40″ to enhancethe contact surface between the implant 40″ and the subchondral bone100. It should be understood that the taper lock ring 360, washer 361,and sutures 363 described with respect to this embodiment allow theimplant to be noncannulated but still easily handled. These elements arenot required to be constructed as illustrated herein, and may bereplaced by adhesive components, suction components, or other componentsserving the same function.

[0198] As FIGS. 21 and 22 illustrate, a unitary (one-piece) implant 400may also be constructed, thereby obviating the need for a fixationscrew, taper lock ring, washer, and suture. In this embodiment, implant400 has key-shaped portion 401 for engagement with a reciprocalkey-shaped surface 411 in an aperture 412 at the defect site 410, aplurality of barbs 402 (or other mating features, e.g., one or morethreads, ribs, fins, milled slots, tapered distal features, features toprevent rotational movement of the implant, or features to increasefriction between the implant and the aperture at the defect site) forproducing outward tension within the aperture 412 at the defect site 410and for increasing the contact surface area of the implant 400 withrespect to the aperture 412 at the defect site 410. In this embodiment,an aperture 412 having a key-shaped surface 411 or other feature formating with the implant is created directly in the defect site 410, byboring, abrasion, or other techniques for forming an appropriatelyshaped aperture in the chondral bone 410 for receiving an implant 400having a corresponding key-shaped or other mating feature 401. It shouldalso be recognized that, in this or other embodiments, the fixationscrew could be replaced with a tensioned member attachment, e.g.,anchored to the distal femoral cortex. Alternatively, the fixation screwcould be configured as a guide wire, only to define the axis AAcorresponding to an axis about the point of origin in the implant to beused (as shown in FIGS. 14c and 19 c), but not to provide mechanicalanchoring to or for the implant.

[0199]FIG. 23 illustrates other alternative embodiments for an implantconsistent with the invention, showing a perspective view of thecomponents of an exemplary composite implant, in one embodiment of thepresent invention. As shown, implant 500 comprises top 501 and bottom502 portions. Top portion 501 has a bottom surface 503 which may beglued, welded, bonded, or otherwise attached to top surface 504 ofbottom portion 502, while bottom surface 505 of bottom portion 502comprises the patient geometry and is the load-bearing surface of theimplant, as set forth hereinabove. Top 504 and bottom 505 surfaces ofthe bottom portion 502 may comprise, in whole or in part, bioengineeredmaterial, while top portion 501 may comprise a material such astitanium. In such a configuration, top portion 501 may be fabricatedand/or manufactured (e.g. in large quantities) as a universal, generic,standard supply item for medical practitioners, which merely needs to beattached to a custom-machined bottom portion 502 comprising thepatient-specific geometry. Surfaces 503 and 504 may be flat or maycomprise other mating features, shapes or configurations.

[0200] Further composite implant embodiments are illustrated in FIG. 24,wherein implant 600 comprises the patient-specific geometry 603 and auniform thickness material bottom portion 602 comprising the bottom orbearing surface 606. The bottom surface 603 of top portion 601 mateswith the top surface 604 of bottom portion 602, and surfaces 603 and 604may be flat or may comprise other mating features, shapes orconfigurations. Lip 605 of bottom portion 602 has an inside diametersubstantially the same as the outside diameter of top portion 601, sothat top portion 601 fits slidably into bottom portion 602, whereby thetwo portions 601 and 602 may be glued, welded, bonded, or otherwiseattached to one another. Bottom surface 606, being of uniform thickness,reflects the patient-specific geometry which surface 603 comprises andis the load-bearing surface of the implant.

[0201] Other materials from which an implant consistent with theinvention may be constructed, in whole or in part, include ceramic, e.g.aluminum oxide or zirconium oxide; metal and metal alloys, e.g.Co—Cr—W—Ni, Co—Cr—M, CoCr alloys, CoCr Molybdenum alloys, Cr—Ni—Mnalloys, powder metal alloys, 316L stainless steel, Ti 6A1 −4V ELI;polymers, e.g., polyurethane, polyethylene (wear resistant andcross-linked), thermoplastic elastomers; biomaterials, e.g.polycaprolactone; and diffusion hardened materials, e.g. Ti-13-13,Zirconium and Niobium. Coatings used may include, e.g., porous coatingsystems on bone-contacting surfaces, hydrophilic coatings onload-bearing surfaces, hydroxyapatite coatings on bone-contactingsurfaces, and tri-calcium phosphate on bone-contacting surfaces.Additionally, components of the invention may be molded or cast,hand-fabricated, or machined.

[0202] Alternatively, measurement methods may be utilized whereby radiusmeasurements are taken with respect to an axis AA corresponding to anaxis about the point of origin in the implant to be used (as shown inFIGS. 14c and 19 c). The technique is used in reverse, whereby aimingdevices are used to place axis AA with respect to prefabricatedgeneric-geometry implants.

[0203] It is noted that, although the invention is herein described asutilizing a single reference axis, multiple reference axes may be usedfor measuring, mapping, or cutting a single defect or an articularsurface having multiple defects, as well as for fabricating a singleimplant, or multiple implants for a single articular surface, consistentwith the invention. In other embodiments, methods for mapping the defectand/or articular surface other than those described hereinabove arepossible, e.g., MRI or CT scanning, fluoroscopy, ultrasound, bonedensity, other stereotactic systems, nuclear medicine, or other sound orlight wave-based imaging methods.

[0204] It is further noted that, although the invention is describedherein as utilizing the specific geometry of a patient's articularsurface to fabricate an implant for that patient, it is contemplatedthat data from a plurality of patients may be analyzed statistically andutilized in fabricating and/or manufacturing (e.g. in large quantities)one or more universal, generic, or standard supply item type implantsfor medical practitioners to use in a procedure consistent with theinvention. For such implants, as well as for patient-specific implantsas described herein, pre- or post-implantation trimming may be requiredto correct for minor variations that may occur as between the implantand the subchondral bone (or other articular surface).

[0205] It should be understood that, although the various toolsdescribed hereinabove, e.g., for measuring, cutting, and seating, aredescribed as separate devices, a single handle, shaft and/or instrumentmay be configured to serve as a universal mounting tool for a series ofdevices for performing various functions consistent with the invention.

[0206] Generic Bone Resurface Implant, Cutting Tool, and Procedure

[0207]FIGS. 27a-48 depict another exemplary embodiment of the presentinvention. In this embodiment a generic bone implant (or set ofstandardized implants) is created (or selected) based on developing anaxis normal to the surface and collecting only one data point. In theabove-described embodiments, a non-normal axis was utilized, and fourdata points were required to develop ML and AP curves. Further, ageneric cutting tool is used to cut the bone at this site to a pointwhere a generic implant can be used. Several improved tools relating tothe procedure for using such an implant (as well as for using implantsas described hereinabove) are further described in this section andillustrated in the corresponding figures.

[0208]FIG. 27a depicts an exemplary drill guide device 700 according tothis exemplary embodiment. The guide 700 includes a contact surface 702of known diameter d on the distal end 708 of the guide, where diameter dis generally the width of the widest portion of the site of the lesion.The distal end 708 of the guide is generally a hollowed-out toroidalstructure attached to a handle 706. A central lumen 704 runs the lengthof the guide from the attachment point of the distal end 708 to thehandle 706, and through the handle 706. The guide device may beconstructed in a number of other ways, including, e.g., a distal end 708comprising a transparent material, e.g., polycarbonate or another clearplastic. For example, as shown in FIG. 27b, a guide device 700′ maycomprise a distal end 708′ (which could comprise either an opaque or atransparent material) having a plurality of cutaway areas 743 to improvevisibility and the accuracy of drill location with respect to the siteof a lesion. The guide device may also comprise a tripod-likeconstruction, or other construction comprising fins, or projections. Itshould be noted that, instead of a central lumen being used to locatethe working axis, a cylindrical bore located at some distal location ofthe guide may serve to create a working axis that is not necessarilycoaxial to the handle or connecting shaft of the instrument.

[0209] Referring now to FIGS. 28a and 28 b, the present embodimentoperates on the assumption that to a first approximation an anatomicalmodel of some articular surfaces (e.g., knee, hip, etc.) can be assumedto be locally spherical. In other words, as shown in FIGS. 28a and 28 b,the AP plane and ML plane, respectively, are depicted, wherein eachcorresponds to a model of the articular surface of a femoral region.These figures break up these cross-sections into a plurality of radii ofarcs defining the articular surface, i.e., R₁-R₄ in the AP plane, andR₅-R₇ in the ML plane. In this embodiment, the inventors herein havefound that surfaces in some regions can be assumed to be substantiallylocally spherical. Thus, for example, the present embodiment assumesthat R₃ approximately equals R₆ (i.e., R₃ is within 50% of R₆). Underthese assumptions, a normal axis can easily be developed. Oncedeveloped, one data point then needs to be defined to obtain therelevant geometry of an implant, as will be described below. If R₃ isnot within 50% of R₆, an alternative method for developing an axisnormal to the surface of the lesion site, as described hereinbelow withreference to FIGS. 49-53, may be used.

[0210] FIGS. 29-34 depict the use of the drill guide, the genericimplant, and procedures therefor, according to this exemplaryembodiment. In FIG. 29, the drill guide 700 is brought up to a lesionsite 712 of the articular surface 710. The guide 700 is positioned sothat the distal end 702 covers the lesion site 712, such that thecontact surface of the distal end 702 makes contact at a plurality ofpoints around the lesion site 712 on the articular surface 710. As shownin FIG. 30, with slight pressure the guide 700 becomes stable and fixedon the articular surface 710. Once seated in position, a guide pin 714is driven through the central lumen of the guide to create a workingaxis that is generally normal to the articular surface 710 at the pointof contact of the guide pin. As FIG. 31 illustrates, a standard boredrill (not shown) can be placed over the guide pin 714 to create a pilothole 716 for the screw (not shown).

[0211] With reference now to FIG. 32, as with the previous embodimentsdescribed above, a screw 720 is driven into the pilot hole 716. A cap722 having a male component 719 adapted to mate with the female taper718 of the screw 720 is placed on the screw 720. The screw is driven tothe appropriate depth, such that the top surface of the cap 722 issubstantially aligned with the articular surface 710, within the lesionsite 712, thereby ensuring congruency of the implant to the joint.Turning now to FIG. 33, the cap 722 is removed, and a rod 730 having amating taper 731 on its distal tip is inserted into the screw 720. Theguide 700 is positioned over the rod 730 so that the distal end 702covers the lesion once again. As illustrated in FIG. 34, since thelength of the rod 730 and the length of the guide 700 are known, ameasurement of the exposed end length of the rod (l) may be taken. Thiswill provide the information needed with respect to the implantgeometry, by indicating the distance between the seating depth in thescrew and the tangent point of the implant surface. As shown in FIG. 35,since the axis, z, is defined (by the drill guide) as normal to thesurface of the implant at a plurality of points, all dimensions definingthe AP and ML curves may be assumed to be equal, such that only onedimension, 1, is left to define the implant geometry. Variations fromknee to knee and within a knee may be reflected in changes in l. Forexample, the implant 736 of FIG. 36 may be compared to the implant 737of FIG. 37. For implant 736 of FIG. 36, the value of l₁ represents arelatively “flat” region on the articular cartilage, where the radius ofthe arc R_(AC1) is a relatively large number. However, for implant 737of FIG. 37, the value of l₂ represents a more curved region on thearticular cartilage, where the radius of the arc R_(AC2) is a smallernumber than R_(AC1). As indicated by clinical data, there is a range ofvalues for 1 that suggests 5 to 6 values of l that will fit a majorityof people. Thus, generic, off-the-shelf sized implants may be made. Asingle procedure technique involving establishing the normal axis,measuring l, and selecting the appropriate size implant is thereforefeasible.

[0212] As illustrated in FIG. 38, an exemplary cutting or reaming tool740 (e.g., as described hereinabove with respect to FIGS. 15b and 16) isused to prepare the lesion site 712 to receive the implant (not shown).The cutting or reaming tool 740 may be configured so that, when coupledto the axis defined by the guide pin, it can be used for cuttingoperations. The tool 740 may have a cannulated shaft and a distal offsetarm having a cutting or blade surface (not shown) having a radiuscorresponding to the radius of the implant to be used, such that thearticular cartilage may be circumscribed by rotation of the tool 740 forcleanly cutting the surrounding articular cartilage in preparation forreceiving the implant. The tool 740 may be configured so that, whencoupled to the axis defined by the guide pin, it can be used for cuttingoperations. The proximal face of the screw 720 may serve as a depth stopfor the proximal portion of the tool 740, thereby defining acutting/reaming depth corresponding to the thickness of the implant, l.

[0213] Those skilled in the art will recognize that the cutting tool maybe motorized in certain embodiments, and/or alternatively, asillustrated in FIG. 39, an exemplary cutting tool 744 may comprise acannulated shaft 749, a circular blade portion 745 having a leading edge746 comprising a blade surface turned on the distal-most portion. Such atool 744 may further comprise a handle portion 747 and may be adapted tobe turned by hand by the operator of the tool by means of rotating thehandle 747, or alternatively, may be motorized in certain embodiments.

[0214]FIG. 40 illustrates an exemplary cleaning tool 770 for cleaningthe female taper (not shown) of the screw 720 prior to delivery of theimplant. The distal end 771 of an exemplary cleaning tool 770 comprisesa semi-rigid material formed into a shape adapted to enter into thefemale taper of the screw 720 and be manipulated by the operator of thetool, to remove tissue or other debris therefrom, thereby ensuring agood mate of the female taper 720 of the screw and the male taper of theimplant to be delivered (not shown).

[0215] FIGS. 41-43 illustrate an exemplary suction tool 760 for holdingthe implant by means of a suction force and delivering it to the lesionsite, as well as the steps of an exemplary procedure for using thesuction tool 760 to deliver an implant. As illustrated in FIG. 41, anexemplary suction tool 760 comprises an elastomeric suction tip 761 atits distal portion 767, a proximal surface 768, an inlet 762 for matingwith a suction tube 763 connected either to a hospital wall suctionsupply 764 or other suction system, and a switch or valve 765 forcontrolling the suction force. As FIG. 42 illustrates, when the suctionforce at the elastomeric suction tip 761 is activated by the switch orvalve 765, the implant 742 is held in place, and thus, the suction tool760 may be used to hold the implant prior to, and during, the deliverythereof. As shown in the cross-sectional view of FIG. 43, the distalportion 767 of an exemplary suction tool 760 may comprise a rigid tip766 (which may comprise, e.g., plastic material) disposed within theelastomeric suction tip 761. Force may be applied to the rigid tip 766(e.g., by striking or pressing on the proximal surface 768 of the tool760) in order to seat the implant 742 within the lesion site, once themale taper 769 of the implant 742 and its corresponding matingcomponent(s) 778 are properly aligned with the female taper of the screw(not shown) and its corresponding mating component(s). Since the suctiontip 761 is elastomeric (e.g., rubber), upon application of such force,the material will compress, allowing impact to be transferred to theimplant 742 for purposes of seating it. It is noted that, in addition toits utility in delivering an implant, a suction tool 760 as describedherein (or a suction tool similar thereto) might also be used at somepoint during the process of removing an implant (e.g., in the event theimplant is not fully seated).

[0216]FIG. 44 illustrates an exemplary implant 742 driven into thelesion site 712 of the articular surface 710 once the site 712 has beensufficiently reamed or cut.

[0217]FIG. 45 illustrates an exemplary implant removal or revision tool750 comprising a shaft portion 751 and a distal portion 753, and FIG. 46is a cross-sectional view illustrating the exemplary tool 750 with aremoved implant 742 being held in place therein. As shown, the distalportion 753 of the tool 750 may comprise an approximately cylindricalstructure with a circular blade portion 752 having a leading edge 758comprising a blade surface turned on the distal-most portion and a lipportion 755 disposed proximally with respect to the leading edge 758. Aplurality of slits 754 parallel to the longitudinal central axis of thedistal portion 753 are disposed along the length of the cylindricalstructure, so as to permit sufficient outward expansion of the distalportion 753 to accommodate the top edge of the implant 742 therein.Thus, when the distal portion 753 of the tool 750 is forced onto animplant 742 to be removed, and driven down over the implant 742, thedistal portion 753 will snap/lock into place once the lip portion 755 ofthe distal portion 753 of the tool 750 passes the top edge of theimplant 742 being removed, thereby holding the implant 742 in placewithin the distal portion 753 of the tool 750, as shown in FIG. 46. Atthis point, a device such as a slap-hammer or slide hammer (not shown)may be used to unseat the implant 742. An exemplary such device maycomprise a shaft having a weight slidably disposed thereon, wherein oneend of the shaft is connected to the proximal end (not shown) of thetool 750 and the other end of the shaft comprises a stop for preventingthe weight from moving off the shaft, and wherein the weight ispropelled away from its connection point with the proximal end of thetool 750, such that it stops abruptly at the stop and exerts a pullingforce on the implant.

[0218] Alternative Embodiment of Screw

[0219]FIGS. 47 and 48 illustrate an exemplary alternatively-keyedembodiment of the screw 720′ (c.f., key feature 315 of screw 10′, asshown in FIG. 9c) and the exemplary alternatively-keyed implant 742′ towhich it is adapted to mate. As shown, the male taper 769′ of theimplant 742′ is coupled at its distal end to an offset mating feature778′ for mating with a corresponding offset mating feature 779 of thescrew 720′. The mating feature 778′ of the implant 742′ comprises agenerally cylindrical structure (and may further comprise a rounded orchamfered distal end portion 777′ and/or other geometric features, i.e.,recesses and/or protrusions) and is both offset from the centrallongitudinal axis of, and diametrically smaller than, the male taper769′ of the implant 742′. As FIG. 48 illustrates, a generallycylindrical recessed mating feature 779 (or similar mating recess(es)and/or protrusion(s), e.g., a rounded or chamfered distal end portion780) corresponding to the offset distal mating feature 778′ of theimplant 742′ is disposed within the innermost portion of the femaletaper 718′ of the implant 742′, and offset from the central longitudinalaxis of the female taper 718′. The female mating feature 779 of thescrew is provided to mate with the offset male distal mating feature778′ of the implant 742′, so as to seat the taper 769′ of the implant742′ at a fixed location within the screw 720′, thereby preventingrotation of the implant 742′ with respect to the screw 720′. Along withthe mating features 778′, 779, the taper structures provided may serveto prevent movement of the implant 742′ with respect to the screw 720′in all directions. A screw 720′ consistent with the present inventionmay comprise a titanium alloy, e.g., a 316L stainless steel alloy or acobalt-chrome alloy.

[0220] Alternative Method for Developing Axis Normal to Lesion SiteSurface FIGS. 49-53 illustrate an alternative method for developing anaxis normal to the surface of the lesion site using a biaxial measuringtool. This method has particular utility for lesion sites where theradii of arcs defining the articular surface, R_(ML) and R_(AP), aredifferent, i.e., the region is not locally spherical. (This would be thecase, e.g., if R₃ is not within 50% of R₆, as illustrated in FIGS. 29aand 29 b and described hereinabove.) To develop an axis normal to thesurface, a biaxial measuring tool 800 is provided. The tool 800comprises an outer shaft 805 coupled fixedly to an outer component 801having a set of arms 803, and an inner shaft 806 slidably disposedwithin the outer shaft 805, wherein the inner shaft is coupled fixedlyto an inner component 802 having a set of arms 804. The arms 803, 804 ofthe outer 801 and inner 802 components may take several forms, and oneexemplary form for the arms 803, 804 is illustrated in FIGS. 49-53,wherein the distal portion of each arm 803, 804 tapers outward andconnects to one of four contact portions 808. The contact portions 808may be, e.g., as shown, one of four arcuate sections of a generallytoroidal member (which may be solid or hollow) having a generallycircular cross-section. (The lengths of the arcuate sections do notnecessarily need to be equal to one another, e.g., as illustrated in theexemplary contact portions 808 of FIGS. 49-53, the arcuate lengths ofthe contact portions 808 corresponding to the inner component 802 areshorter than those contact portions 808 corresponding to the outercomponent 801.) The inner shaft 806 may be biased forward so as to tendto extend from the outer shaft 805, or may alternatively be advancedmanually without spring bias. The inner component 802 is slid proximallyor distally with respect to the outer component 801, until all of thecontact portions 808 make contact with the articular surface (notshown). In this manner, the articular surface curvatures may beseparated into AP elements and ML elements, such that four separatecontact points may be extrapolated from the four contact portions 808,based on the relative positions of the inner 802 and outer 801components, and an axis normal to the surface of the lesion site may bedefined. The shaft of the tool 800 may be cannulated (not shown), so asto allow a guide pin or wire (or a boring tool) to pass therethrough andinto the articular surface, as described hereinabove with respect toFIGS. 27a to 31. As shown in FIG. 53, if the inner 802 and outer 801components are aligned such that the four contact portions 808 meet toform a complete toroidal member or ring, the articular surface must belocally spherical, i.e., R_(ML) and R_(AP) (as shown in FIG. 49) areequal, and it is therefore not necessary to use the biaxial tool 800.

[0221] It should be noted that, alternatively, contact surfaces may beconstructed of some pliable, or malleable material(s) so thatindependently moving rigid mechanical members are not necessary. As longas the contact surfaces provide a normalizing force to some centralshaft when the contact surfaces are applied to the articular surface, anormal axis could be defined.

[0222] In another embodiment, this biaxial guide could be replaced by aseries of sized “trials” or gauges of predefined surfaces of varyingdimensions, which are simply pressed onto the articular surface tovisually determine an appropriate fit. These gauges may resemble animplant, as described herein, without any features (e.g., fixationelement or screw) on the underside, and may contain a handling tab orother element for holding the gauge. The contact surfaces of thesegauges may have a circular cross section, an ovular cross section, oranother cross-section comprising a plurality of points to surround adefect in an articular surface, and the plurality of points may or maynot lie in the same plane. Although they may be less precise or lessaccurate than other measuring methods described herein, it iscontemplated that implant selection could be made directly from thesegauges.

[0223] Digital Measuring System

[0224] FIGS. 54-61 illustrate an exemplary digital measuring systemconsistent with the present invention. As shown, the system 810comprises a base unit 811 coupled to the handpiece 812 via a cable 813.As described further hereinbelow, the base unit 811 may comprise a tearstrip 814 in or on the chassis for detaching a printed paper tapecomprising measurement data. Such a system may reduce or eliminatepotential for surgical or other human error with respect to theimplementation of the present invention.

[0225]FIG. 55 is an exploded view of an exemplary handpiece 812 in adigital system consistent with the present invention. The linearmeasuring elements of the handpiece 812 are nested concentrically andcoaxially to the rotary measuring elements, so that when the probeassembly 818 is translated and rotated with respect to the main body 822of the handpiece, the 0 and z dimensions are simultaneously recorded.The handpiece 812 comprises a main body 822 containing a linear readinghead 813 coupled to a linear reader 814, a linear index strip 815, arotary reading head 821 coupled to a rotary reader 816, and a rotaryindex strip 817. The probe assembly 818 comprises a contact tip 819coupled to an inner shaft 820 running along the length of the handpiece813 disposed within the main body 822. The shaft 820 comprises a matingfeature 834 at its distal end that is keyed to fit in the mating featureof an implanted screw, such that the shaft 820 provides a rotationalaxis. The shaft 820 is rigidly connected to the main body 822 of thehandpiece 812 via a nut 823 at its rear. The handpiece 813 is coupledto, and transfers motion both rotationally and axially from, the contacttip 819 via the shaft 820. In this manner, the linear 815 and rotary 817strips, which may comprise, e.g., mylar polyester film having thereon avery fine printed pattern, pass through the linear 813 and rotary 821reading heads, respectively, such that the heads 813, 821 read thepattern on the strips 815, 817 and output data representing therotational and axial travel of the contact tip 819.

[0226] Exemplary strips and heads may include those manufactured by U.S.Digita™ Corporation of Vancouver, Wash., USA. FIG. 55a is a cutaway viewillustrating an exemplary printed linear index strip 815 passing throughan exemplary linear head 813 for reading, and FIG. 55b is a cutaway viewillustrating two alternative exemplary printed rotary index strips 817,817′ of varying sizes passing through an exemplary rotary head 821 forreading. FIG. 55c illustrates an exemplary linear index strip 815comprising concentric “bullseye” circles 830, reference lines 831, atext area 832, and a pattern area 833. FIG. 55d illustrates an exemplaryrotary index strip 817 comprising an opaque area 823, index areas 824, apattern area 825, a text area 826, crosshairs 827, concentric “bullseye”circles 828 and a central aperture 829.

[0227] Turning now to FIGS. 56a and 56 b, a rotational groove 840 and alinear groove 841 are provided on the handpiece 812, such that the probeassembly 818 may slide onto the shaft 820 of the handpiece 812 and snapinto the linear 841 and rotational 840 grooves.

[0228]FIGS. 57 and 58 illustrate top and side views, respectively, ofthe assembled exemplary handpiece 812.

[0229]FIGS. 59 and 60 illustrate top and side cross-sectional views,respectively, of the assembled exemplary handpiece 812.

[0230]FIG. 61 illustrates a cutaway view of an exemplary base unit 811in an exemplary digital measuring system consistent with the presentinvention. The base unit 811 comprises a power supply 850 (the systemmay be battery or AC-line powered), a paper roll 851, a thermal printer852, a feed loop dowel 853 for threading the paper roll 851 into thethermal printer 852, a set of controls or buttons 854, and one or moredisplays 855 (e.g., LED/LCD). The base unit 811 further comprisesappropriate hardware and/or software to compare measured values to knownvalues, as well as to compare sweeps to one another to ensure proceduralaccuracy. Further, the displays 855 and/or paper printouts from thethermal printer 852 may be adapted to display to the user, based onmeasured data, the ideal size of the generic implant to use. If a customimplant is required, a printout of the data set may be generated usingthe printer 852. The base unit 811 may further comprise other means ofrecording data (not shown), e.g., floppy disk, hard disk, memory/flashcard, etc., and may further comprise appropriate hardware to provideoutput signals (e.g., via RS-232, USB, etc.) to external hardware.Instead of the strips, heads, and other recording elements described inthe exemplary digital system hereinabove, other digital measurementmethods may be used, including reflective light or sound methods, andpercutaneous methods (e.g., using a hypodermic needle in conjunctionwith an MRI, CT, ultrasound, or other scanning method, wherein theneedle or other handheld device comprises sensing elements for mappingthe articular surface).

[0231] It should be noted that in the digital measuring system andmethod described hereinabove (as well as any of the mapping/measuringtechniques herein), a second (or third, etc.) set of data points may betaken, and the subsequent set(s) of data points compared with theoriginal data points taken, to reduce the margin of error from takingonly a single set of data points. Thus, a software algorithm in a systemor method consistent with the invention may comprise appropriateroutines to effect such comparisons, for error reduction purposes.

[0232] Those skilled in the art will recognize that the presentinvention is subject to other modifications and/or alterations, all ofwhich are deemed within the scope of the present invention, as definedin the hereinafter appended claims.

What is claimed is:
 1. A guide device for locating a working axissubstantially normal with respect to an articular surface of bone, saiddevice comprising: a shaft having an end and an aiming feature forprojecting an axis; and a contact surface comprising a plurality ofpoints radially extending from the aiming feature of said shaft; whereinsaid plurality of points of said contact surface surrounds a defect inan articular surface.
 2. A guide device as claimed in claim 1, whereinsaid contact surface is formed by a generally toroidal member coupled tothe end of said shaft.
 3. A guide device as claimed in claim 1, whereinsaid contact surface comprises at least one fin, projection, ordeformable element.
 4. A guide device as claimed in claim 1, whereinsaid shaft is cannulated, and wherein said guide device is adapted toreceive a tool for creating a pilot hole through said cannulated shaftand permit said tool to be driven substantially normal into an articularsurface of bone when at least three of said plurality of points of saidcontact surface make contact with said articular surface of bone.
 5. Aguide device as claimed in claim 1, wherein said guide device is adaptedto receive a guide pin or wire through said aiming feature and permitsaid guide pin or wire to be driven substantially normal into anarticular surface of bone when at least three of said plurality ofpoints of said contact surface make contact with said articular surfaceof bone.
 6. A guide device as claimed in claim 1, wherein said contactsurface comprises at least one aperture or transparent portion formedtherein, permitting the viewing of at least a portion of an articularsurface therethrough.
 7. A guide device as claimed in claim 1, whereinsaid plurality of points of said contact surface corresponds to theplurality of points making contact with an articular surface along theperimeter of an implant.
 8. A guide device as claimed in claim 1,wherein said plurality of points of said contact surface corresponds tothe plurality of points along the perimeter of a portion of an articularsurface to be removed.
 9. A guide device for locating a working axissubstantially normal with respect to an articular surface of bone, saiddevice comprising: a shaft having an aiming feature for projecting anaxis; and a contact surface comprising a plurality of points radiallyequidistant from the aiming feature of said shaft.
 10. A guide devicefor locating a working axis substantially normal with respect to anarticular surface of bone, said device comprising: a shaft having anaiming feature for projecting an axis; and a contact surface comprisinga plurality of points equidistant from the aiming feature of said shaft.11. A guide device for locating a working axis substantially normal withrespect to an articular surface of bone, said device comprising: a shafthaving an end and a central longitudinal axis; and a contact surfacecomprising a plurality of points radially equidistant from said centrallongitudinal axis.
 12. A guide device for locating a working axissubstantially normal with respect to a non-spherical articular surfaceof bone, said device comprising: a first element having a longitudinalaxis and a contact surface mounted to a shaft; and a second element witha contact surface movable with respect to the contact surface of thefirst element, wherein, when said guide device is placed on anon-spherical articular surface, both contact surfaces make contact withsaid articular surface.
 13. A guide device as claimed in claim 12,wherein each said contact surface comprises a plurality of arcuatesections of a generally toroidal member, wherein said generally toroidalmember is formed when said contact surfaces make contact with a locallyspherical articular surface.
 14. A guide device as claimed in claim 12,wherein one said contact surface is biased in one direction with respectto the other said contact surface.
 15. A guide device as claimed inclaim 12, wherein said contact surfaces are adapted such that thecontact surface of the first element make contact with a plurality ofpoints along either one of the AP or ML curves of an articular surface,while the contact surface of said second element make contact with aplurality of points along the other of the AP or ML curves of saidarticular surface.
 16. A guide device as claimed in claim 12, whereinsaid first or said second element comprises a cannula, wherein saidguide device is adapted to receive a tool for creating a pilot holethrough said cannula and permit said tool to be driven substantiallynormal into an articular surface of bone.
 17. A guide device as claimedin claim 12, wherein said first or said second element comprises acannula, wherein said guide device is adapted to receive a guide pin orwire through said cannula and permit said guide pin or wire to be drivensubstantially normal into an articular surface of bone.
 18. A guidedevice as claimed in claim 12, wherein said first or said second elementcomprises at least one aperture or transparent portion formed therein,permitting the viewing of at least a portion of an articular surfacetherethrough.
 19. A guide device as claimed in claim 12, wherein theoutermost dimensions of said contact surfaces surround a defect in anarticular surface.
 20. A guide device as claimed in claim 15, whereinthe plurality of points contacting said contact surfaces corresponds tothe plurality of points abutting an articular surface along theperimeter of an implant.
 21. A guide device as claimed in claim 15,wherein the plurality of points contacting said contact surfacescorresponds to the plurality of points along the perimeter of a portionof an articular surface to be removed.
 22. A guide device for locating aworking axis substantially normal with respect to an articular surfaceof bone having an anterior-posterior (AP) curve and a medial-lateral(ML) curve, said device comprising: a cannulated outer shaft, said outershaft having a central longitudinal axis and an outer component at itsdistal end, said outer component comprising a set of arms; and acannulated inner shaft slidably disposed within the cannula of saidouter shaft, said inner shaft having an inner component at its distalend and sharing the central longitudinal axis of said outer shaft, saidinner component comprising a set of arms.
 23. A method for replacing aportion of an articular surface of bone, said method comprising:establishing a working axis substantially normal to an articular surfaceof bone; excising only a portion of said articular surface adjacent saidaxis, thereby creating an implant site; and installing an artificialimplant into said implant site.
 24. A method as claimed in claim 23,wherein said implant comprises a bone-facing distal surface adapted tomate with said implant site, said surface comprising at least one matingfeature; and a proximal surface having a contour substantially matchingor based on the original surface contour of said excised portion of saidarticular surface.
 25. A method as claimed in claim 24, wherein saidmating feature is selected from the group consisting of: barbs, threads,ribs, fins, milled slots, tapered distal features, features to preventrotational movement of said implant, or features to increase frictionand/or contact surface between said implant and the aperture at saidimplant site.
 26. A method for replacing a portion of an articularsurface of bone, said method comprising: establishing a working axissubstantially normal to an articular surface of bone; excising only aportion of said articular surface adjacent said axis, thereby creatingan implant site; selecting an implant corresponding to the dimensions ofsaid implant site from a set of variously-sized implants; and installingsaid selected implant into said implant site.
 27. A method as claimed inclaim 26, wherein said establishing step is performed using a toolcomprising a shaft having an aiming feature and a distal surfacecomprising a plurality of points radially extending from said aimingfeature.
 28. A method as claimed in claim 26, wherein said implantcomprises a bone-facing distal surface adapted to mate with said implantsite, said surface comprising at least one mating feature; and aproximal surface having a contour substantially matching or based on theoriginal surface contour of said excised portion of said articularsurface.
 29. A method as claimed in claim 28, wherein said matingfeature is at least one of the features selected from the groupcomprising: barbs, threads, ribs, fins, milled slots, tapered distalfeatures, features to prevent rotational movement of said implant, orfeatures to increase friction between said implant and the aperture atsaid implant site.
 30. A method as claimed in claim 26, wherein saidestablishing step is performed using a tool comprising a shaft having anend and an aiming feature; and at least one contact surface coupled tothe end of said shaft, said contact surface comprising a plurality ofpoints radially extending from said aiming feature.
 31. A method asclaimed in claim 26, wherein said establishing step is performed byinstalling a guide pin or wire into said articular surface along saidaxis.
 32. A method as claimed in claim 26, wherein said excising step isperformed using a cutting tool that rotates about said axis.
 33. Amethod as claimed in claim 26, wherein said installing step comprisesdriving a fixation element into said articular surface along said axis.34. A method as claimed in claim 33, wherein said fixation elementcomprises a mating feature at its proximal end.
 35. A method as claimedin claim 33, wherein said fixation element comprises a screw.
 36. Amethod as claimed in claim 34, wherein said fixation element is adaptedto mate, position, or align with an element adapted to aid in thedepthwise positioning of said fixation element with respect to saidarticular surface.
 37. A method as claimed in claim 34, wherein saidmating feature is adapted to mate, position, or align with the distalportion of an implant.
 38. A method as claimed in claim 37, wherein saidmating feature is adapted to prevent movement of said implant withrespect to said fixation element.
 39. A method as claimed in claim 33,wherein said fixation element comprises a tapered distal feature and/oraggressive distal threads.
 40. A method for replacing a portion of anarticular surface of bone generally defined by a first and a secondcurve, said method comprising: establishing an axis generally normal tothe portion of an articular surface of bone to be replaced based on afirst curve and a second curve of said articular surface; excising onlya portion of said articular surface adjacent said axis, thereby creatingan implant site; fabricating an artificial implant corresponding to thedimensions of said implant site; and installing said artificial implantinto said implant site.
 41. A method as claimed in claim 40, whereinsaid implant comprises a bone-facing distal surface adapted to mate withsaid implant site, said surface comprising at least one mating feature;and a proximal surface having a contour substantially matching or basedon the original surface contour of said excised portion of saidarticular surface.
 42. A method as claimed in claim 41, wherein saidmating feature is selected from the group consisting of: barbs, threads,ribs, fins, milled slots, tapered distal features, features to preventrotational movement of said implant, or features to increase frictionbetween said implant and the aperture at said implant site.
 43. A methodfor replacing a portion of an articular surface of bone generallydefined by a first and a second curve, said method comprising:establishing an axis generally normal to the portion of an articularsurface of bone to be replaced based on a first curve and a second curveof said articular surface; excising only a portion of said articularsurface adjacent said axis, thereby creating an implant site; selectingfrom a set of variously-sized artificial implants an artificial implantcorresponding to the dimensions of said implant site; and installingsaid selected implant into said implant site.
 44. A method as claimed inclaim 43, wherein said first and second curves are anterior-posterior(AP) and medial-lateral (ML) curves.
 45. A method as claimed in claim43, wherein said excising step is performed by cutting at least aportion of said articular surface radially symmetrically about saidaxis.
 46. A method as claimed in claim 43, wherein said implantcomprises a bone-facing distal surface adapted to mate with said implantsite, said surface comprising at least one mating feature; and aproximal surface having a contour substantially matching or based on theoriginal surface contour of said excised portion of said articularsurface.
 47. A method as claimed in claim 46, wherein said matingfeature is selected from the group consisting of: barbs, threads, ribs,fins, milled slots, tapered distal features, features to preventrotational movement of said implant, or features to increase frictionbetween said implant and the aperture at said implant site.
 48. A methodas claimed in claim 43, wherein said establishing step is performedusing a tool comprising a first element having an aiming feature and acontact surface mounted to a shaft, and a second element with a contactsurface movable with respect to the contact surface of the firstelement, wherein, when said tool is placed on a non-spherical articularsurface, both contact surfaces make contact with said articular surface.49. A method as claimed in claim 43, wherein said establishing step isperformed by installing a guide pin or wire into said articular surfacealong said axis.
 50. A method as claimed in claim 43, wherein saidexcising step is performed using a cutting tool that rotates about saidaxis.
 51. A method as claimed in claim 43, wherein said installing stepcomprises driving a fixation element into said articular surface alongsaid axis.
 52. A method as claimed in claim 51, wherein said fixationelement comprises a mating feature at its proximal end.
 53. A method asclaimed in claim 51, wherein said fixation element comprises a screw.54. A method as claimed in claim 52, wherein said mating feature isadapted to mate, position, or align with an element adapted to aid inthe depthwise positioning of said fixation element with respect to saidarticular surface.
 55. A method as claimed in claim 52, wherein saidmating feature is adapted to mate with the distal portion of an implant.56. A method as claimed in claim 55, wherein said mating feature isadapted to prevent movement of said implant with respect to saidfixation element.
 57. A method as claimed in claim 51, wherein saidfixation element comprises a tapered distal feature and/or aggressivedistal threads.
 58. A tool for holding an implant, said tool comprising:at least one element adapted for connection to an activatable suctionsource; and an elastomeric suction tip adapted to receive an implant,said tip being coupled to said at least one element.
 59. A tool asclaimed in claim 58, further comprising a rigid tip disposed within theelastomeric suction tip, whereby a force in the direction of thedelivery site of said implant permits said rigid tip to contact saidimplant while said implant is being held by said suction tip.
 60. Amethod for holding an implant comprising: coupling a suction source toan implant; and activating said suction source.
 61. A method fordelivering an implant comprising: coupling an active suction source toan implant; approximating said implant to its delivery site; andapplying a force to said implant in the direction of said delivery site.62. A tool for removing an implant from its delivery site, said toolcomprising: an element with a generally leading edge and a barb elementdisposed proximally to the leading edge; and at least one structuralelement that creates sufficient bias of the leading edge of the tool torigidly couple to a surface of the implant to be removed.
 63. A tool asclaimed in claim 62, further comprising means for coupling said tool toa slap hammer or slide hammer capable of applying a pulling force to animplant held at said barb element.
 64. A tool for removing an implantfrom its delivery site, said tool comprising: a cylindrical structurehaving an end; said end comprising a longitudinal central axis, acircular blade portion having a leading edge comprising a blade surfaceturned on the distal-most portion, and a lip portion disposed proximallywith respect to the leading edge; and a plurality of slits parallel tothe longitudinal central axis of said end formed along the length ofsaid cylindrical structure, so as to permit sufficient outward expansionof the distal end to accommodate the top edge of an implant therein. 65.A tool as claimed in claim 64, further comprising means for couplingsaid tool to a slap hammer or slide hammer capable of applying a pullingforce to an implant held in said distal end.
 66. A method for removingan implant from its delivery site, said method comprising: disposing thelip portion of the leading edge of the end of a removal tool over theupper edge of an implant seated in its delivery site; and applying apulling force to said removal tool.
 67. A method as claimed in claim 66,wherein said pulling force is applied using a slap hammer or slidehammer.
 68. A device for measuring a portion of an articular surface ofbone, said device comprising: a handpiece; a shaft disposed within saidhandpiece, said shaft comprising a feature for aligning with a workingaxis or mating to a fixed element; a contact tip moveably coupled tosaid shaft; and at least one measuring element coupled to said contacttip or said shaft.
 69. A device as claimed in claim 68, furthercomprising recording means for recording measurements taken by said atleast one measuring element.
 70. A device as claimed in claim 69,wherein translation and/or rotation of the contact tip with respect tothe handpiece or shaft causes said at least one measuring element tomeasure travel of the contact tip, and the recording means to record atleast one measurement taken by at least one said measuring element. 71.A device as claimed in claim 70, further comprising machine-readablecode to analyze said at least one recorded measurement and output to auser the dimensions of an implant to be used in said articular surface.72. A device as claimed in claim 70, further comprising machine-readablecode to analyze said at least one recorded measurement and compare saidmeasurement to at least one previously taken measurement.
 73. A deviceas claimed in claim 70, further comprising machine-readable code toanalyze said at least one recorded measurement, select an implantcorresponding to said at least one measurement from a set ofvariously-sized implants, and output to a user said selection.
 74. Adevice for mapping a portion of an articular surface of bone, saiddevice comprising: a handpiece; an inner shaft running along the lengthof and disposed within said handpiece, said inner shaft comprising amating feature for mating with a fixed element located substantiallynormal with respect to an articular surface; a contact tip slidably androtatably disposed about said inner shaft; a rotary measuring elementcoupled to and rotating with said contact tip; and a linear measuringelement nested concentrically and coaxially to said rotary measuringelement, and coupled to and moving linearly with said contact tip.
 75. Adevice as claimed in claim 74, further comprising recording means forrecording measurements taken by said measuring elements.
 76. A device asclaimed in claim 75, wherein translation and/or rotation of the contacttip with respect to the handpiece or shaft causes said measuringelements to measure travel of the contact tip, and the recording meansrecords measurements taken by the measuring elements simultaneously,when the mating feature of said inner shaft is mated with said fixedelement and/or said contact tip is fixably aligned to a working axis.77. A device as claimed in claim 76, further comprising machine-readablecode to analyze said recorded measurements and output to a user thedimensions of an implant to be used in said articular surface.
 78. Adevice as claimed in claim 76, further comprising machine-readable codeto analyze said recorded measurements, select an implant correspondingto said measurements from a set of variously-sized implants, and outputto a user said selection.
 79. A set of guide devices for locating aworking axis substantially normal with respect to an articular surfaceof bone or for determining the dimension of an implant to be installedin an articular surface of bone, said set comprising: a plurality ofvariously dimensioned guide devices, each said guide device having ahandling tab or shaft and a contact surface; said contact surfacecomprising a plurality of points radially extending from said handlingtab or shaft; wherein, when at least one said guide device is placed onan articular surface, said contact surface makes contact with saidarticular surface, and said plurality of points of said contact surfacesurrounds a defect in said articular surface.
 80. A set of guide devicesas claimed in claim 79, wherein said plurality of points of at least onesaid guide device do not all lie in the same plane.